Apparatus for detecting a physical quantity acting as an external force and method for testing and manufacturing this apparatus

ABSTRACT

A sensor comprises a semiconductor pellet ( 10 ) including a working portion ( 11 ) adapted to undergo action of a force, a fixed portion ( 13 ) fixed on the sensor body, and a flexible portion ( 13 ) having flexibility formed therebetween, a working body ( 20 ) for transmitting an exerted force to the working portion, and detector means ( 60-63 ) for transforming a mechanical deformation produced in the semiconductor pellet to an electric signal to thereby detect a force exerted on the working body as an electric signal. A signal processing circuit is applied to the sensor. This circuit uses analog multipliers ( 101-109 ) and analog adders/subtractors ( 111-113 ), and has a function to cancel interference produced in different directions. Within the sensor, two portions (E 3,  E 4 -E 8 ) located at positions opposite to each other and producing a displacement therebetween by action of a force are determined. By exerting a coulomb force between both the portions, the test of the sensor is carried out. Further, a pedestal ( 21, 22 ) is provided around the working body ( 20 ). The working body and the pedestal are located with a predetermined gap or spacing therebetween. A displacement of the working body is caused to limitatively fall within a predetermined range corresponding to the spacing. The working body and the pedestal are provided by cutting a same common substrate ( 350, 350 ′).

This application is a division of Ser. No. 07/761,771 filed Aug. 14,1991, now U.S. Pat. No. 5,295,386, which is a 371 of PCT/JP90/91688,filed Dec. 26, 1990.

TECHNICAL FIELD

This invention relates to an apparatus for detecting a physical quantityacting as an external force, e.g., a force exerted on a working body, anacceleration exerted on a weight body, or a magnetism exerted on amagnetic body. Particularly, this invention relates to a signalprocessing circuit, a testing method, and a manufacturing method for aforce sensor serving as a main part of such a detector, and a structureof this force sensor.

BACKGROUND ART

In recent years, there are proposed force sensors including, arranged ona semiconductor substrate, resistance elements having a property of thepiezo resistive effect that the electric resistance varies in dependencyupon a mechanical deformation to detect a force from changes inresistance values of the resistance elements. Further, accelerationsensors or magnetic sensors to which such force sensors are applied arealso proposed. In either detector, a strain generative body partiallyhaving flexibility is used to detect a mechanical deformation producedin the strain generative body as changes in electric resistance of theresistance elements. A working body is provided for exerting a force onthe strain generative body. If a weight body responsive to accelerationis used as the working body, an acceleration sensor is provided.Further, if a magnetic body responsive to magnetism is used as theworking body, a magnetic sensor is provided.

For example, in U.S. Pat. No. 4,905,523, U.S. patent application Ser.No. 295,210, No. 362,399, No. 470,102, and No. 559,381,force/acceleration/magnetic sensors according to the invention of theinventor of this application are disclosed. Further, in U.S. Pat.application Ser. No. 526,837, a novel manufacturing method for a sensorof this kind is disclosed.

The force sensors disclosed in these patent materials can detect adirection and a magnitude of an external force applied to apredetermined working point on the basis of changes in resistance valuesof resistance elements formed on a single crystal substrate. If a weightbody is formed at the working point, it is also possible to detect, as aforce, an acceleration exerted on the weight body. Accordingly, thispermits application as an acceleration sensor. Further, if a magneticbody is formed at the working point, it is also possible to detect, as aforce, magnetism exerted on the magnetic body. Accordingly, this permitsapplication as a magnetic sensor.

However, the conventional force sensors (or acceleration sensors, ormagnetic sensors based on the same principle) have the problem thatthere may occur interference in the output characteristic with respectto respective axial directions of two-dimensions or three-dimensions.For example, in the case of the three dimensional acceleration sensor,components in the X-axis, Y-axis and Z-axis directions of anacceleration exerted on a predetermined working point must beindependently detected, respectively. In the case of conventionalsensors, however, these components in respective axial directionsinterfere with each other. As a result, a detected value of thecomponent in one axial direction was influenced to some extent bydetected values of components in other axial directions. Such aninterference is not preferable because it lowers reliability of measuredvalues.

With the above in view, a first object of this invention is to provide asignal processing circuit capable of obtaining correct detected valuesfree from interference of the components in other axial directions.

In order to mass produce such sensors to deliver them on the market, itis necessary to conduct a test or inspection at the final stage of themanufacturing process. The test for the force sensor can be carried outrelatively with ease. Namely, this test may be accomplished by applyinga force of a predetermined magnitude to the working point in apredetermined direction to check a detected output at this time.However, the test for the acceleration sensor or the magnetic sensorbecomes more complicated. Since the sensor body is in a sealed state, itis necessary to check detected outputs while actually exerting, from theexternal, acceleration or magnetism thereon. Particularly, in the caseof the acceleration sensor, it is the present state that a vibrationgenerator is used to give vibration to the sensor body to carry out atest. This results in the problem that the testing device becomes large,and a test for a dynamic acceleration of vibration is only conducted.

With the above in view, a second object of this invention is to providea testing method capable of more easily testing a sensor having aworking body of force such as an accelerating sensor or a magneticsensor, and to provide a sensor having a function capable of immediatelycarrying out this testing method.

Further, conventionally proposed sensors using resistance elements has aproblem in the case of carrying out high sensitivity measurement. Forexample, in the case of the acceleration sensor, it is sufficient forthe purpose of utilizing collision detection of a vehicle, etc. to havea function to detect acceleration of the order of 10 to 100 G on thefull scale. However, in order to detect a swing by hand of a camera, toconduct a suspension control for a vehicle, and to conduct a control foran antilock brake system for a vehicle, it is necessary to detect anacceleration of the order of 1 to 10 G. For carrying out such a highsensitivity acceleration detection, it is necessary to increase theweight of a working body having a function to produce a force on thebasis of an acceleration. However, in the case of the structure ofconventional sensors, it was difficult to enlarge the working boby.

In the case of the high sensitivity sensor, where a large force morethan a predetermined limit is applied thereto, the danger that thesemiconductor substrate may be damaged is increased. For this reason, itis necessary to provide, around the working body, a member for allowingdisplacement of the working body to limitatively fall within apredetermined range. This gives another problem that the structurebecomes complicated.

Further, in the case of detecting force, acceleration, and magnetism,etc. exerted in three-dimensional directions, there would occur adifference between a detection sensitivity in a direction parallel tothe surface of the semiconductor substrate and that in a directionperpendicular thereto. The fact that a sensitivity difference occurs independency upon the direction of detection is not particularlypreferable for high sensitivity sensors.

With the above in view, a third object of this invention is to provide asensor using resistance elements suitable for higher sensitivityphysical quantity measurement, and a method of manufacturing such asensor.

DISCLOSURE OF INVENTION

I Feature relating to the first object

To achieve the first object to provide a signal processing circuitcapable of obtaining a correct detected value free from interference ofthe components in other axial directions, this invention has thefollowing features.

(1) The first feature resides in a signal processing circuit for asensor in which when an external force is exerted on a predeterminedworking point in an XYZ three-dimensional coordinate system, amechanical deformation is produced on a single crystal substrate by theexternal force, the sensor detecting a component in the X-axis directionAx, a component in the Y-axis direction Ay, and a component in theZ-axis direction Az of the external force exerted on the working pointon the basis of electric signals Vx, Vy and Vz produced due to themechanical deformation,

wherein coefficients K11, K12, K13, K21, K22, K23, K31, K32 and K33 aredetermined so that the relational equations expressed below hold betweenAx, Ay, Az, Vx, Vy and Vz:

Ax=K11Vx+K12Vy+K13Vz

Ay=K21Vx+K22Vy+K23Vz

Az=K31Vx+K32Vy+K33Vz

and the values of terms of the right sides of the relational equationsare computed by using analog multipliers, and a computation betweenrespective terms of the right sides of the relational equations isperformed by using analog adders/subtracters, thus to provide detectedvalues Ax, Ay and Az from these computed results.

(2) The second feature resides in a signal processing circuit for anacceleration detector in which when an external force is exerted on apredetermined working point, a mechanical deformation is produced on asingle crystal substrate by the external force, the detector detecting acomponent in an X-axis direction Ax and a component in a Y-axisdirection perpendicular thereto of an external force exerted on aworking point on the basis of electric signals Vx and Vy produced due tothe mechanical deformation,

wherein coefficients K11, K12, K21 and K22 are determined so that therelational equations expressed below hold between Ax, Ay, Vx and Vy:

Ax=K11Vx+K12Vy

Ay=K21Vx+K22Vy

and the values of terms of the right sides of the relational equationsare computed by using analog multipliers, and a computation betweenrespective terms of the right sides of the relational equations isperformed by using analog adders/subtracters, thus to provide detectedvalues Ax and Ay from these computed results.

(3) The third feature resides in a signal processing circuit for a forcesensor in which a plurality of resistance elements exhibiting the piezoresistive effect that the electric resistance varies in dependency upona mechanical deformation are arranged on a single crystal substrate, andwhen an external force is exerted on a predetermined working point in anXYZ three-dimensional coordinate system and a mechanical deformation isproduced by the external force, the sensor detecting a component in theX-axis direction Ax, a component in the Y-axis direction Ay, and acomponent in the Z-axis direction Az of an external force exerted on aworking point on the basis of voltage values Vx, Vy and Vz obtained onthe basis of a bridge circuit constituted by the plurality of resistanceelements,

wherein coefficients K11, K12, K13, K21, K22, K23, K31, K32 and K33 aredetermined so that the relational equations expressed below hold betweenAx, Ay, Az, Vx, Vy and Vz:

Ax=K11Vx+K12Vy+K13Vz

Ay=K21Vx+K22Vy+K23Vz

Az=K31Vx+K32Vy+K33Vz

and the values of terms of the right sides of the relational equationsare computed by using analog multipliers, and a computation betweenrespective terms of the right sides of the relational equations isperformed by using analog adders/subtracters, thus to provide detectedvalues Ax, Ay and Az from these computed results.

(4) The fourth feature resides in a signal processing circuit for anacceleration detector in which a plurality of resistance elementsexhibiting the piezo resistive effect that the electric resistancevaries in dependency upon a mechanical deformation, and when an externalforce is exerted on a predetermined working point, a mechanicaldeformation is produced on a single crystal substrate by the externalforce, the detector detecting a component in an X-axis direction Ax anda component in a Y-axis direction Ay perpendicular thereto of anexternal force exerted on a working point on the basis of respectivebridge voltage values Vx and Vy of two sets of bridge circuitsconstituted by the plurality of resistance elements,

wherein coefficients K11, K12, K21 and K22 are determined so that therelational equations expressed below hold between Ax and Ay and Vx andVy:

Ax=K11Vx+K12Vy

Ay=K21Vx+K22Vy

and the values of terms of the right side of the relational equationsare computed by using analog multipliers, and a computation betweenrespective terms of the right sides of the relational equations isperformed by using analog adders/subtracters, thus to provide detectedvalues Ax and Ay from these computed results.

In accordance with the above described signal processing circuit, acharacteristic matrix showing the condition of interference producedbetween components in respective axial directions and an inversecharacteristic matrix of the inverse matrix thereof are determined inadvance. Further, corrective operations using this inversecharacteristic matrix are carried out, thereby making it possible tocancel the influence of interference. Furthermore, since thesecorrective operations are all carried out at the analog computationcircuit, the circuit configuration becomes simple and a correctioncircuit can be realized at a low cost. In addition, because operation isperformed in an analog form, the operation speed becomes high, givingrise to no inconvenience even in the case of measuring an instantaneousphenomenon.

II Feature relating to the second object

To achieve the second object to provide a simple testing method withrespect to each sensor, this invention has the following features.

(1) The first feature resides in a method of testing a sensor, thesensor comprising:

a strain generative body including a working portion adapted to undergoaction of a force, a fixed portion fixed to a sensor body, and aflexible portion having flexibility formed between the working portionand the fixed portion,

a working body for transmitting an applied force to the working portion,and

detector means for transforming a mechanical deformation produced in thestrain generative body by the transmitted force to an electric signal tothereby detect, as an electric signal, a force exerted on the workingbody,

wherein the method comprises the steps of determining a first portionand a second portion located at positions opposite to each other andproducing a displacement therebetween, exerting a coulomb force betweenboth the portions, and testing the sensor on the basis of the exertedcoulomb force and a detected result by the detector means.

In accordance with the first feature, a coulomb force is exerted betweenthe first and second portions. By this coulomb force, the first portionundergoes displacement relative to the second portion to induce amechanical deformation in the strain generative body. Accordingly, thesame state as the state where an external force is exerted on theworking body can be created. Thus, test of the sensor can be carried outwithout actually applying an external force thereto.

(2) The second feature resides in, in the method having the abovedescribed first feature,

a method in which a first electrode layer is formed at the first portionand a second electrode layer is formed at the second portion to carryout a test conducted while exerting a repulsive force between the firstand second electrode layers by applying voltages of the same polarity tothe both electrode layers, respectively, and a test conducted whileexerting an attractive force between the first and second electrodelayers by applying voltages of polarities different from each otherthereto, respectively.

In accordance with the second feature, by applying a voltage across twoopposite electrode layers, a coulomb force can be exerted. In addition,by selecting the polarity of an applied voltage, the coulomb force canbe exerted as either a repulsive force or an attractive force. Thus, thetest having higher degree of freedom can be conducted.

(3) The third feature resides in a method of testing a sensor, thesensor comprising:

a strain generative body including a working portion adapted to undergoaction of a force, a fixed portion fixed to a sensor body, and aflexible portion having flexibility formed between the working portionand the fixed portion,

a working body for transmitting an applied force to the working portion,and

detector means for transforming a mechanical deformation produced in thestrain generative body by the transmitted force to an electric signal tothereby detect, as an electric signal, a force exerted on the workingbody,

wherein the method comprises the steps of determining a first planesurface and a second plane surface located at positions opposite to eachother to produce a displacement therebetween by the action of the force,forming an electrode layer on the first plane surface, and forming, onthe second plane surface, a plurality of electrically independentelectrode layers at a plurality of portions,

the method further comprising the steps of applying a voltage of a firstpolarity to the electrode layer on the first plane surface, andselectively applying, every electrode layers, a voltage of a firstpolarity or a voltage of a second polarity opposite to the firstpolarity to the respective electrode layers on the second plane surfaceto exert a coulomb force of a repulse force or an attractive forcebetween the electrode layer on the first plane surface and the electrodelayers on the second plane surface, and thereafter conducting test ofthe sensor on the basis of the applied coulomb force and a detectedresult by the detector means.

In accordance with the third feature, since one electrode layer isdivided into a plurality of subelectrode layers, an approach is employedto select the polarity of an applied voltage, thereby making it possibleto carry out a test in which a coulomb force is exerted in variousdirections.

(4) The fourth feature resides in an acceleration sensor comprising:

a strain generative body including a working portion adapted to undergoaction of a force, a first portion fixed to a sensor body, and aflexible portion having flexibility formed between the working portionand the fixed portion,

a weight body adapted to undergo action of a force by an accelerationapplied to the sensor body, the weight body transmitting the force thusexerted to the working portion and allowing the stain generative body toproduce a mechanical deformation,

a resistance element having the property that the resistance valuevaries in dependency upon a mechanical deformation produced in thestrain generative body,

a first electrode layer formed on a first plane surface to produce adisplacement by action of an acceleration,

a second electrode layer formed on a second plane surface opposite tothe first plane surface, and

wiring means for connecting the resistance element, the first electrodelayer and the second electrode layer to an external electric circuit,

to apply a predetermined voltage to the first and second electrodelayers to exert a coulomb force between both the electrode layers,thereby permitting the strain generative body to produce a mechanicaldeformation even in the state where no acceleration is exerted.

In accordance with the fourth feature, within the acceleration sensor,two electrode layers for carrying out the test according to the abovedescribed first feature are formed, and wiring therefor is implemented.Accordingly, by only connecting a predetermined electric circuit to thisacceleration sensor, the test can be carried out.

(5) The fifth feature resides in a magnetic sensor comprising:

a strain generative body including a working portion adapted to undergoaction of a force, a fixed portion fixed to a sensor body, and aflexible portion having flexibility formed between the working portionand the fixed portion,

a magnetic body adapted to undergo action of a force by a magnetic fieldwhere the sensor body is placed, the magnetic body transmitting theforce thus exerted to the working portion and allowing the straingenerative body to produce a mechanical deformation,

a resistance element having the property that the resistance valuevaries in dependency upon a mechanical deformation produced in thestrain gtenerative body,

a first electrode layer formed on a first plane surface to produce adisplacement by action of a magnetic force,

a second electrode layer formed on a second plane surface opposite tothe first plane surface, and

wiring means for connecting the resistance element, the first electrodelayer and the second electrode layer to an external electric circuit,

to apply a predetermined voltage to the first and second electrodelayers to exert a coulomb force between both the electrode layers,thereby permitting the strain generative body to produce a mechanicaldeformation even in the state where no magnetic force is exerted.

In accordance with the fifth feature, within the magnetic sensor, twoelectrode layers for carrying out the test according to the abovedescribed first feature are formed, and wiring therefor is implemented.Accordingly, by only connecting a predetermined electric circuit to thismagnetic sensor, the test can be carried out.

(6) The sixth feature is directed to a sensor having the above describedfourth or fifth feature, characterized in that one of the first andsecond electrode layer is constituted with a single electrode layer, andthe other electrode layer is constituted with a plurality ofelectrically independent subelectrode layers, to select the polaritiesof voltages applied to the respective subelectrode layers, therebypermitting a mechanical deformation produced in the strain generativebody to have directivity.

In accordance with the sixth feature, since one electrode layer isconstituted with a single electrode layer, and the other electrode layeris constituted with a plurality of subelectrode layers, selection of thepolarities of applied voltages is made, thereby making it possible toconduct a test in which a coulomb force is exerted in variousdirections.

(7) The seventh feature is directed to a sensor having the abovedescribed sixth feature, characterized in that the other electrode layeris constituted with two electrically independent subelectrode layers toselect the polarities of voltages applied to respective subelectrodelayers, thereby allowing the strain generative body to produce amechanical deformation with respect to a direction of a line connectingthe centers of two subelectrodes layers, and a mechanical deformationwith respect to a direction perpendicular to the surfaces of the twosubelectrode layers.

In accordance with the seventh feature, since two subelectrode layersare provided, a test in which a coulomb force is exerted with respect totwo directions perpendicular to each other can be conducted.

(8) The eighth feature is directed to a sensor having the abovedescribed sixth feature, characterized in that the other electrode layeris constituted with four electrically independent subelectrode layers,and these subelectrode layers are arranged at respective end pointpositions of two orthogonal line segments so as to select the polaritiesof voltages applied to the respective subelectrode layers, therebyallowing the strain generative body to produce a mechanical deformationwith respect to a direction of a first line segment of the two linesegments, and a mechanical deformation with respect to a directionperpendicular to the surfaces of the four subelectrode layers.

In accordance with the eighth feature, since four subelectrode layersare provided in a crossing manner, a test in which a coulomb force isexerted with respect to three directions perpendicular to each other canbe conducted.

(9) The ninth feature is directed to a sensor having the above describedfourth or fifth feature characterized in that the first electrode layerand the second electrode layer are constituted with a plurality ofelectrically independent first subelectrode layers and a plurality ofelectrically independent second subelectrode layers, respectively, so asto select polarities of voltages applied to the respective subelectrodelayers, thereby permitting a mechanical deformation produced in thestrain generative body to have directivity.

In accordance with the ninth feature, selection having higher degree offreedom can be made. Thus, a test in which a coulomb force is exerted invarious directions can be conducted.

III Feature relating to the third object

To achieve the third object to provide a sensor suitable for a highersensitivity physical quantity measurement and a method of manufacturingsuch a sensor, this invention has the following features.

(1) The first feature resides in a sensor comprising:

a substrate wherein a working portion, a flexible portion and a fixedportion are defined substantially at the center of the substrate, aroundthe working portion and around the flexible portion, respectively, todig a groove in the flexible portion on the lower surface of thesubstrate, or to form a through hole in the flexible portion of thesubstrate to thereby allow the flexible portion to have flexibility anda resistance element is formed of which electric resistance varies onthe basis of a mechanical deformation of the flexible portion on theupper surface of the substrate so as to detect changes in the electricresistance of the resistance element, produced on the basis of adisplacement relative to the fixed portion of the working portion,

a working body for transmitting a force to the working portion beingconnected to the lower surface of the working portion,

a pedestal for supporting the fixed portion being connected to a firstportion on the lower surface of the fixed portion,

wherein a second portion on the lower surface of the fixed portion and aportion on the upper surface of the working body being constituted sothat they are opposite to each other with a predetermined spacingtherebetween, a displacement in an upper direction of the working bodybeing permitted to limitatively fall within a predetermined range by thesecond portion.

In accordance with the first feature, the central portion on the uppersurface of the working body is connected to the lower surface of theworking portion of the substrate, but the side portion of the workingbody extends to the portion below the fixed portion of the substrate.Accordingly, it is possible to make a design so that the volume of theworking body is large as a whole. As a result, the weight of the workingbody is increased, thus making it possible to improve sensitivity withease. Further, since the side portion of the working body extends up tothe portion below the fixed portion of the substrate, it is possible tolimit a displacement in an upper direction of the working body by makinguse of the fixed portion lower surface of the substrate as a controlmember. Accordingly, the necessity of individually providing a controlmember in an upper direction is eliminated, thus permitting thestructure to be simple.

(2) The second feature is directed to a sensor having the abovedescribed first feature,

wherein the inside surface of the pedestal and the outside surface ofthe working body are constituted so that they are opposite with apredetermined spacing therebetween, thus making it possible to allow adisplacement in a lateral direction of the working body to limitativelyfall within a predetermined range by the inside surface of the pedestal.

In accordance with the second feature, in addition to the first feature,the inside surface of the pedestal and the outside surface of theworking body are constituted so that they are opposite to each otherwith a predetermined spacing therebetween. For this reason, it ispossible to limit a displacement in a lateral direction of the workingbody by making use of the inside surface of the pedestal as a controlmember. Accordingly, the necessity of individually providing a limitmember in a lateral direction is eliminated, thus permitting thestructure to be simple.

(3) The third feature is directed to a sensor having the first or secondfeature,

wherein the pedestal is fixed onto a predetermined control surface sothat the control surface and the lower surface of the working body areopposite to each other with a predetermined spacing therebetween, thusmaking it possible to allow a displacement in a lower direction of theworking body to limitatively fall within a predetermined range by thecontrol surface.

(4) The fourth feature resides in a sensor comprising:

a substrate wherein a working portion, a flexible portion and a fixedportion are defined substantially at the center of the substrate, aroundthe working portion and around the flexible portion, respectively, todig a groove in the flexible portion on the lower surface of thesubstrate, or to form a through hole in the flexible portion of thesubstrate to thereby allow the flexible portion to have flexibility anda transducer is formed for transforming a mechanical deformation to anelectric signal at the flexible portion on the upper surface of thesubstrate so as to detect changes in an electric surface produced on thebasis of a displacement relative to the fixed portion of the workingportion to thereby detect a physical quantity exerted on the workingportion,

a working body for transmitting a force to the working portion beingconnected to the lower surface of the working portion,

wherein, when it is assumed that a perpendicular is drawn downward fromthe center of gravity G of the working body onto the upper surface ofthe substrate, the relationship expressed as L<r holds between a lengthL of the perpendicular and a distance r from the foot P of theperpendicular up to the outside portion of the groove.

This fourth feature is based on the fact that the inventor of thisapplication has found an optimum range in respect of a distance betweena working point defined at the central portion on the upper surface ofthe substrate and the center of gravity of the working body. Thisoptimum range satisfies such condition that sensitivities with respectto all directions substantially become uniform at the time of detectinga physical quantity in a three dimensional direction. For this reason, asensor in which three is no difference between detection sensitivitiesdependent upon direction can be realized.

(5) The fifth feature resides in a method of manufacturing a sensorusing resistance elements,

the method comprising the steps of:

defining a flexible area in the form of a square ring having a width ona first substrate,

defining a working area and a fixed area at one of the portion insidethe square ring and the portion outside the square ring and at the otherportion, respectively,

forming resistance elements within the flexible area on a first planesurface of the first substrate,

digging a groove in the form of parallel crosses in correspondence withthe square ring position on a second plane surface of the firstsubstrate to form, in the flexible area, a groove in the form of squarecomprised of a portion of the groove in the form of parallel crosses,thus allowing the flexible area to have flexibility,

connecting a first plane surface of a second substrate to the secondplane surface of the first substrate, and

cutting the second substrate to thereby form a working body connected tothe working area of the first substrate and comprised of a portion ofthe second substrate, and a pedestal connected to the fixed area of thefirst substrate and comprised of a portion of the second substrate.

In accordance with the fifth feature, a groove in the form of square isformed in the flexible area on the second plane surface of the firstsubstrate. Since the groove in the form of square can be easily formedby digging a groove in the form of parallel crosses by mechanicalprocessing, it is possible to efficiently form a precise groove.Further, the weight body or the magnetic body is formed by a portion ofthe second substrate, and the pedestal for supporting the firstsubstrate is formed by another portion. Namely, prior to carrying outthe dicing process, the weight body or the magnetic body and thepedestal can be formed every wafer.

(6) The sixth feature resides in a method of manufacturing a sensorusing resistance elements,

the method comprising the steps of:

defining a plurality of unit areas on a first substrate, and, withineach unit area, defining a flexible area in the form of a square ringhaving a width, and defining a working area and a fixed area at one ofthe portion inside the square ring and the portion outside the squarering and at the other portion, respectively,

forming resistance elements in each flexible area on a first planesurface of the first substrate,

digging a plurality of grooves on the side of a second plane surface ofthe first substrate in a longitudinal direction and in a lateraldirection, respectively, to form four grooves along four boundary sidesof the working area or the fixed area, thus allowing the flexible areasto have flexibility by these grooves,

connecting a first plane surface of the second substrate to the secondsurface of the first substrate,

cutting the second substrate to thereby form, within each unit area, aworking body connected to the working area of the first substrate andcomprised of a portion of the second substrate, and a pedestal connectedto the fixed area of the first substrate and comprised of a portion ofthe second substrate, and

cutting off, every unit area, the first and second substrates to formsensors independent each other.

In accordance with the sixth feature, a plurality of unit areas aredefined on the first substrate, and the processing proceeds at the sametime with respect to respectively plurality of unit areas. Finally, oneunit area will constitute one sensor unit. A plurality of grooves aredug in a longitudinal direction and in a lateral direction on the secondplane surface of the first substrate, respectively. Within each unitarea, respective four grooves are formed along four boundary sides ofthe working area or the fixed area. By these grooves, flexibility isgiven to the flexible area. Since it is sufficient to form grooveslongitudinally and laterally in a matrix form, these grooves can beeasily dug by mechanical processing. Thus, precise grooves can beefficiently formed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of an acceleration sensor subject tothe application of this invention,

FIG. 2 is a top view of a semiconductor pellet serving as the center ofthe sensor of FIG. 1,

FIG. 3 is a top view of a weight body and a pedestal of the sensor ofFIG. 1,

FIG. 4 is a top view of a lower part control member of the sensor ofFIG. 1,

FIG. 5 is a bottom view of an upper part control member of the sensor ofFIG. 1,

FIGS. 6a to 6 c are circuit diagrams of a bridge constructed withrespect to the sensor of FIG. 1, respectively,

FIGS. 7a to 7 c show stress distriburion diagrams when a force in theX-axis direction is exerted on the sensor shown in FIG. 1, respectively,

FIGS. 8a to 8 c show stress distribution diagrams when a force in theY-axis direction is exerted on the sensor shown in FIG. 1, respectively,

FIGS. 9a to 9 c show stress distribution diagrams when a force in theZ-axis direction is exerted on the sensor shown in FIG. 1, respectively,

FIG. 10 is a table showing the detecting operation of the sensor shownin FIG. 1,

FIG. 11 is a block diagram of a single processing circuit for anacceleration detector according to this invention,

FIG. 12 is a block diagram of a signal processing circuit for anotheracceleration detector according to this invention,

FIG. 13 is an actual circuit diagram of a multiplier used in the signalprocessing circuit of this invention,

FIG. 14 is an actual circuit diagram of an adder used in the signalprocessing circuit of this invention,

FIG. 15 is a circuit diagram of an actual circuit both serving as amultiplier and an adder used in the signal processing circuit of thisinvention,

FIG. 16 is an actual partial circuit diagram of a signal processingcircuit for an acceleration detector according to this invention,

FIG. 17 is a perspective view showing the state where an electrode layeris formed on the weight body and the pedestal of the sensor of FIG. 1,

FIG. 18 is a top view showing the state where an electrode layer isformed on the semiconductor pellet of the sensor of FIG. 1,

FIG. 19 is a cross sectional view showing the state where electrodelayers are formed on respective portions of the center portion of thesensor of FIG. 1,

FIGS. 20 to 22 are cross sectional views showing displacement states ofthe center portion of the sensor of FIG. 1, respectively,

FIG. 23 is a top view showing the state where practical electrode layersare formed on the semiconductor pellet of the sensor of FIG. 1,

FIG. 24 is a cross sectional view showing the state where practicalelectrode layers are formed at predetermined portions,

FIG. 25 is a cross sectional view showing the state where electrodelayers according to a different embodiment are formed at predeterminedportions of the center portion of the sensor of FIG. 1,

FIG. 26 is a top view showing the state where electrode layers accordingto a further different embodiment are formed on the semiconductor pelletof the sensor of FIG. 1,

FIG. 27 is a bottom view showing the state where electrode layersaccording to a different emboiment are formed on the upper part controlmember of the sensor of FIG. 1,

FIG. 28 is a cross sectional view showing the state where electrodelayers according to a further different embodiment are formed atpredetermined portions of the center portion of the sensor of FIG. 1,

FIG. 29 is a cross sectional view showing the state where electrodelayers according to a still further different embodiment are formed atpredetermined portions of the center portion of the sensor of FIG. 1,

FIG. 30a is a model view showing a method of applying voltage in orderto realize the same state as the state where a force in a Z direction isexerted on the weight body of the sensor shown in FIG. 1,

FIG. 30b is a model view showing a method of applying a voltage in orderto realize the same state as the state where a force in a −Z directionis exerted on the weight body of the sensor shown in FIG. 1,

FIG. 31 is a cross sectional view of the structure of an accelerationsensor according to an embodiment of this invention,

FIG. 32 is a perspective view of the center portion of the sensor shownin FIG. 31,

FIG. 33 is a cross sectional view of the detail of the center portionshown in FIG. 32,

FIG. 34 is a top view of the semiconductor pellet 310 shown in FIG. 33,

FIG. 35 is a top view of the weight body 320 and the pedestal 330 shownin FIG. 33,

FIG. 36 is a top view of the control substrate 340 shown in FIG. 33,

FIGS. 37 and 38 are a side cross sectional view and a top view of theauxiliary substrate 350 from which the weight body 320 and the pedestal330 shown in FIG. 35 are basically formed.

FIG. 39 is a view showing the position where the weight body 320 isconnected to the semiconductor pellet 310 shown in FIG. 33,

FIGS. 40 and 41 are a side cross sectional view and a top view showingan auxiliary substrate according to a different embodiment of thisinvention, respectively,

FIGS. 42 and 43 are a side cross sectional view and a bottom viewshowing a semiconductor pellet according to a further differentembodiment of this invention, respectively,

FIG. 44 is a view showing the position where the weight body 310 isconnected to the semiconductor pellet 310′ shown in FIG. 43,

FIG. 45 is a side cross sectional view of the structure of anacceleration sensor according to a further different embodiment of thisinvention,

FIGS. 46 and 47 are cross sectional views of a force sensor according toan embodiment of this invention, respectively,

FIG. 48 is an explanatory view of a conventional air bag system

FIG. 49 is an explanatory view of an air bag system utilizing anacceleration sensor according to this invention,

FIG. 50 is a view showing the principle of the design of dimensionaccording to this invention,

FIG. 51 is a side cross sectional view showing the structure when atesting method peculiar a sensor according to this invention is applied,and

FIG. 52 is a top view of the control substrate 340 shown in FIG. 51.

BEST MODE FOR CARRYING OUT THE INVENTION

§1 Basic Structure of the Sensor

1.1 Structure of the acceleration sensor

This invention can be widely applied, in general, to an apparatus fordetecting a physical quantity exerted as an external force, and can beutilized not only to a force sensor but also to an acceleration sensor,or a magnetic sensor. In other, words, all sensors are common in thebasic structure to the central portion thereof. Accordingly, the objectof which this invention is applied will be briefly described by takingan example of an acceleration sensor.

FIG. 1 is a structural cross sectional view showing an example of anacceleration sensor. The component serving as the central unit of thissensor is a semiconductor pellet 10. In this example, a single crystalsubstrate of silicon is used. The top view of the semiconductor pellet10 is shown in FIG. 2. The cross section of the semiconductor pellet 10shown at the central portion of FIG. 1 corresponds to the cross sectioncut along the X-axis of FIG. 2. This semiconductor pellet 10 is dividedinto three areas of a working portion 11, a flexible portion 12, and afixed portion 13 in order from the inside toward the outside. Asindicated by broken lines in FIG. 2, an annular groove is formed on theside of the lower surface of the flexible portion 12. The thickness ofthe flexible portion 12 is allowed to be thin by this groove to haveflexibility. Accordingly, when a force is exerted on the working portion11 with the fixed portion 13 being fixed, the flexible portion 12 isbent to produce a mechanical deformation. Thus, the semiconductor pellet10 has a function as a strain generative body. On the upper surface ofthe flexible portion 12, as shown in FIG. 2, resistance elements Rx1 toRx4, Ry1 to Ry4, and Rz1 to Rz4 are formed in predetermined directions,respectively.

As shown in FIG. 1, a weight body 20 is connected at the lower part ofthe fixed portion 13, and pedestals 21 and 22 are connected at the lowerpart of the fixed portion 13. Since a silicon substrate is used as thesemiconductor pellet 10, it is preferable to use borosilicate glass suchas Pyrex, etc., having a coefficient of thermal expansion nearly equalto that of silicon. Further, although not shown in FIG. 1, pedestals 23and 24 are further arranged in a direction perpendicular to planesurface of paper, and pedestals 21 a to 24 a are arranged in an obliquedirection. How they are arranged is clearly shown in FIG. 3 showing theupper surface of only the weight body 20 and the pedestals 21 to 24, and21 a to 24 a. The cross section shown in FIG. 1 corresponds to the crosssection cut along the cutting-plane line 1—1 of FIG. 3. It is to benoted that the reason why the pedestals are arranged in the state asshown in FIG. 3 is due to the fact that the manufacturing processdisclosed in the U.S. patent application Ser. No. 526,837 (EuropeanPatent Application No. 90110066.9) has been carried out. Make referenceto this specification in connection with the detail thereof. A controlmember 30 is connected at the lower parts of the pedestals 21 to 24. Thetop view of the control member 30 is shown in FIG. 4. A square groove 31(the hatched portion in FIG. 4: As describe later, the hatched portionof this figure does not indicate the cross section, but indicates theportion where an electrode is to be formed) is formed on the uppersurface of the control member 30. The cross section shown in FIG. 1corresponds to the cross section along the cutting-plane line 1—1 ofFIG. 4. A control member 40 is fitted over the upper surface of thesemiconductor pellet 10. The lower surface of the control member 40 isshown in FIG. 5. A square groove (the hatched portion in FIG. 5: Asdescribed later, the hatched portion of this figure does not indicatethe cross section, but indicates the portion where an electrode is to beformed) is formed on the lower surface of the control member 40. Thecross section shown in FIG. 1 corresponds to the cross section cut alongthe cutting-plane line 1—1 of FIG. 5.

The bottom surface of the control member 30 is connected to the insidebottom surface of a package 50, as shown in FIG. 1, and thesemiconductor pellet 10 and the weight body 20 are supported by thepedestals 21 to 24, and 21 a to 24 a. The weight body 20 is in a hangingstate within the sensor body. A cover 51 is fitted over the package 50.Bonding pads 14 provided on the semiconductor pellet 10 are electricallyconnected to respective resistance elements within the pellet. Thesebonding pads 14 and leads 52 for external wiring provided on the sidesof the package are connected by means of bonding wires 15.

When an acceleration is applied to this sensor, an external force isexerted on the weight body 20. This external force is transmitted to theworking portion 11. As a result, a mechanical deformation is produced inthe flexible portion 12. Thus, there occur changes in the electricresistance values of the resistance elements. Such changes can be takenout to the external through bonding wires 15 and leads 52. A componentin the X-direction of a force applied to the working portion 11 isdetected by changes in the electric resistance values of the resistanceelements Rx1 to Rx4. A component in the Y-direction thereof is detectedby changes in the electric resistance values of the resistance elementsRy1 to Ry4, and a component in the Z-direction thereof is detected bythe electric resistance values of the resistance elements Rz1 to Rz4.This detection method will be described later.

In the case where this sensor is put into practice as an accelerationsensor, when a large acceleration is applied, an excessive force isexerted on the weight body 20. As a result, a large mechanicaldeformation is produced in the flexible portion 12, resulting in thepossibility that the semiconductor pellet 10 may be broken. To preventsuch a breakage, in the case of the sensor shown in FIG. 1, the controlmembers 30 and 40 are provided. The control member 30 serves to effect acontrol such that a displacement in a lower direction of the weight body20 does not exceed an allowed value, and the control member 40 serves toeffect a control such that a displacement in an upper direction of theweight body 20 (the working portion 11 in practice) does not exceed anallowed value. Further, pedestals 21 to 24 serve to effect a controlsuch that a displacement in a lateral direction of the weight body 20does not exceed an allowed value. Even if an excessive external force isexerted on the weight body 20 to exceed to the above-described allowedvalue so that the weight body 20 attempts to move, the weight body 20collides with these members, so the movement thereof is prevented.Eventually, there is no possibility that a mechanical deformation morethan an allowed value is applied to the semiconductor pellet 10. Thus,the semiconductor pellet 10 is protected from being broken.

As shown in FIG. 2, a plurality of resistance elements R (Rx1 to Rx4,Ry1 to Ry4, Rz1 to Rz4) are formed on the upper surface of thesemiconductor pellet 10. These resistance elements R are resistanceelements having the piezo resistive effect that the electric resistancevaries in dependency upon a mechanical deformation, and are arranged onthe upper surface of the flexible portion 12 in predetermineddirections, respectively. Leads 52 for external wiring are introducedfrom the inside of the package 50 to the outside in a manner to passthrough wiring holes at the side surfaces. The inside terminals of theleads 52 for external wiring are connected to bonding pads 14 (of whichindication is omitted in FIG. 1) provided on the fixed portion 13 of thesemiconductor pellet 10. These bonding pads 14 are connected to theresistance elements R by a wiring pattern (not shown). Accordingly, ifthe leads 52 for external wiring are electrically connected to anexternal control unit (of which indication is omitted), changes in theresistance values of the resistance elements R can be measured by theexternal control unit.

1.2 Operation of the acceleration sensor

Assuming now that an X-axis, a Y-axis and a Z-axis are taken in a rightdirection of FIG. 2, in an upper direction thereof, and in a directionperpendicular to the plane surface of paper (in an upper direction ofthe figure in FIG. 1), respectively, an XYZ three-dimensional coordinatesystem is defined. In this coordinate system, four resistance elementsRx1 to Rx4 are arranged on the X-axis, and are used for detection of anacceleration component in the X-axis direction; four resistance elementsRy1 to Ry4 are arranged on the Y-axis, and are used for detection of anacceleration component in the Y-axis direction; and four resistanceelements Rz1 to Rz4 are arranged along the X-axis in the vicinity of theX-axis, and are used for detection of an acceleration component in theZ-axis direction. While resistance elements Rz1 to Rz4 may be arrangedon an arbitrary axis, it is preferable to arrange them at suitablepositions where crystal dependency of the piezo resistive effect istaken into consideration. As previously described, these respectiveresistance elements R are electrically connected to the external controlunit through leads 52 for external wiring. Within the control unit,bridge circuit as shown in FIGS. 6a to 6 c are constructed with respectto respective resistance elements R. Namely, with respect to resistanceelements Rx1 to Rx4, a bridge circuit as shown in FIG. 6a isconstructed; with respect to resistance elements Ry1 to Ry4, a bridgecircuit as shown in FIG. 6b is constructed; and with respect toresistance elements Rz1 to Rz4, a bridge circuit as shown in FIG. 6c isconstructed. Predetermined voltages or currents are delivered from powersupplies 60 from the bridge circuits, respectively. Thus, bridgevoltages are measured by voltage meters 61, 62 and 63, respectively.

As shown in FIG. 1, the weight body 20 is in a hanging state within acentral portion space encompassed by the peripheral pedestals 21 to 24.When an acceleration is applied to the package 50, an external force isexerted on the weight body 20 due to this acceleration. As a result, theweight body 20 is subjected to displacement from a fixed position.Accordingly, the working portion 11 connected to the weight body is alsosubjected to displacement from the fixed position. A mechanical strainproduced by this displacement is absorbed by a mechanical deformation ofthe flexible portion 12. When there occurs a mechanical deformation inthe flexible portion 12, the electric resistance values of theresistance elements R formed on the flexible portion 12 vary. As aresult, the equilibrium conditions of the bridge circuits shown in FIGS.6a to 6 c are broken, so needles of the voltage meters 61, 62 and 63swing. This is the basic principle of detection of acceleration by thisapparatus.

Now, when resistance elements R are arranged as shown in FIG. 2, anacceleration component in the X-axis direction is detected by thevoltage meter 61, an acceleration component in the Y-axis direction isdetected by the voltage meter 62, and an acceleration component in theZ-axis direction is detected in the bridge circuits of FIGS. 6a to 6 c.The reason therefor will now be described.

FIGS. 7a to 7 c are model views showing stress strain applied to eachresistance element R when a force Fx in the X-axis direction is exertedon the weight body 20. FIG. 7a shows a stress distribution in the crosssection along the resistance elements Rx1 to Rx4, FIG. 7b shows a stressdistribution in the cross section along the resistance elements Ry1 toRy4, and FIG. 7c shows a stress distribution in the cross section alongthe resistance elements Rz1 to Rz4. In these stress distributions, anexpanding direction is indicated by sign + and a contracting directionis indicated by sign −. For example, FIG. 7a shows a stress distributionin the cross section along the resistance elements R1 to R4 when a forceFx in an X-direction is exerted on the weight body 20. The force Fxexerted on the weight body 20 acts as a moment force on the surface ofthe semiconductor pellet 10. As a result, mechanical deformation in acontracting direction are produced with respect to resistance elementsRx1 and Rx3, and mechanical deformations in an expanding direction areproduced with respect to resistance elements Rx2 and Rx4. On thecontrary, with respect to resistance element Ry1 to Ry4, as shown inFIG. 7b, stress does not change. This is because the arrangementdirection (Y-axis direction) of the resistance elements Ry1 to Ry4 isorthogonal to the direction of the force Fx. With respect to resistanceelements Rz1 to Rz4, as show in FIG. 7c, the same changes as those ofthe resistance elements Rx1 to Rx4 occur. Similarly, the stressdistributions produced in respective resistance elements R in the casewhere a force Fy in a Y-axis direction is exerted are shown in FIGS. 8ato 8 c, and the stress distributions produced in respective resistanceelements R in the case where a force Fz in a Z-axis direction is exertedare shown in FIGS. 9a to 9 c. Here, if there is used a resistanceelement having a property such that the resistance value increases withrespect to a mechanical deformation in an expanding direction, and thatthe resistance value decreases with respect to a mechanical deformationin a contracting direction, the relationship between forces Fx, Fy andFz exerted on the weight body 20 and changes in the resistance values ofrespective resistance elements R is as shown in the Table of FIG. 10.Here, sign + and sign − indicate an increase in the resistance value anda decrease in the resistance value, and 0 indicates that the resistancevalue is unchanged.

By making reference to this Table and the bridge circuits of FIGS. 6a to6 c, it will be understood that a force Fx is detected by the voltagemeter 61, a force Fy is detected by the voltage meter 62, and a force Fzis detected by the voltage meter 63. For example, in the case where aforce Fx is exerted, since resistance values of one opposite sides bothincrease, whereas resistance values of the other opposite sides bothdecreases in the bridge circuit of FIG. 6a, the needle of the voltagemeter 61 swings. However, since there is no change in either resistancevalue in the bridge circuit of FIG. 6b, the needle of the voltage meter62 does not swing. In addition, since the resistance values of oneresistance constituting respective opposite sides increases, whereasthose of the other resistance decrease in the bridge circuit of FIG. 6c,they are eventually canceled with each other, so that the needle of thevoltage meter 63 does not swing. Thus, components in respectivecomponents of an accelerated exerted on the detector body are detectedas swings of the needles of the voltage meters 61 to 63.

It is to be noted that while explanation has been given in connectionwith a three dimensional acceleration detector for components in anacceleration direction of all the three axes of XYZ, a two dimensionalacceleration detector for detecting components in an accelerationdirection with respect to two axes of XY, YZ or XZ may be similarlyconstructed. In this case, it is sufficient to provide only resistanceelements and bridge circuits with respect to two axes. Further, whilethere has been shown here the example where three sets of bridges areused to detect respective acceleration components in three axisdirections, this invention can be applied to an apparatus in which twosets of bridges are used to detect respective acceleration components inthree axial directions (e.g., U.S. Pat. No. 4,745,812). In addition,while explanation has been made here by taking an example of anacceleration detector, if a magnetic body is used instead of the weightbody 20, this detector serves as a magnetic detector for detectingmagnetism exerted on a magnetic body, and if there is employed astructure such that an external force is directly exerted to the weightbody 20, the detector serves as a force detector.

§2 Signal Processing Circuit

2.1 Basic principle of the signal processing

A signal processing circuit according to this invention will now bedescribed. As described above, force (or acceleration or magnetism)subject to detection, is detected with respect to the component in theX-axis direction by voltage value Vx at the voltage meter 61, isdetected with respect to the component in the Y-axis direction byvoltage value Vy at the voltage meter 62, and is detected with respectto the component in the Z-axis direction by voltage value Vz at thevoltage meter 63. It is to be noted that, in an apparatus for detectingcomponents in three axis directions by using two sets of bridges,voltage values obtained by performing computation on the basis of bridgevoltage are used as Vx, Vy and Vz in place of bridge voltage themselves.Assuming that respective resistance elements R are arranged as shown inFIG. 2, under the condition where these respective resistance elementsall have the same resistance value and all have the same temperaturecharacteristic, and resistance changes due to distortion are all equalto each other, components in respective axial directions thus detectedare provided as entirely independent detected values from a theoreticalpoint of view, giving rise to no interference. However, in the case ofactually forming respective resistance elements, since such an idealcondition is not provided, interference would occur between detectedvalues. How this interference occurs can be actually measured. Namely,an approach is employed to exert a force (or acceleration or magnetism)having an already known magnitude in a predetermined direction to makean actual measurement of detected values (reads of respective voltagemeters) obtained at this time. As a result, it is known that acharacteristic matrix expressed below is provided: $\begin{bmatrix}{Vx} \\{Vy} \\{Vz}\end{bmatrix} \cdot {\begin{bmatrix}{P11} & {P12} & {P13} \\{P21} & {P22} & {P23} \\{P31} & {P32} & {P33}\end{bmatrix}\quad\begin{bmatrix}{Ax} \\{Ay} \\{Az}\end{bmatrix}}$

where Vx, Vy and Vz are readings of voltage meters 61, 62 and 63,respectively, and Ax, Ay and Az are component values in respectivedirections of a force (acceleration or magnetism) actually exerted.Further P11 to P33 are coefficients constituting the characteristicmatrix. This determinant can be rewritten as follows. $\begin{matrix}{\begin{bmatrix}{Ax} \\{Ay} \\{Az}\end{bmatrix} = \quad {\begin{bmatrix}{P11} & {P12} & {P13} \\{P21} & {P22} & {P23} \\{P31} & {P32} & {P33}\end{bmatrix}^{- 1}\begin{bmatrix}{Vx} \\{Vy} \\{Vz}\end{bmatrix}}} \\{= \quad {\begin{bmatrix}{K11} & {K12} & {K13} \\{K21} & {K22} & {K23} \\{K31} & {K32} & {K33}\end{bmatrix}\quad\begin{bmatrix}{Vx} \\{Vy} \\{Vz}\end{bmatrix}}}\end{matrix}$

Here, the matrix using coefficients K11 to K33 is an inverse matrix ofthe matrix using coefficients P11 to P33. This determinant is written bya general expression as follows:

Ax=K11Vx+K12Vy+K13Vz

Ay=K21Vx+K22Vy+K23Vz

Az=K31Vx+K32Vy+K33Vz

Accordingly, when the above described operation using coefficients K11to K33 is performed with respect to voltage values Vx, Vy and Vzobtained at voltage meters 61 to 63, correct detected values Ax, Ay andAz free from interference can be provided.

2.2 Actual circuit configuration

The signal processing circuit of this invention is constructed toperform this operation by an analog circuit. This circuit is shown, in ablock form, in FIG. 11. Here, Vx, Vy and Vz are analog voltages obtainedat voltage meters 61 to 63, respectively. Blocks 101 to 109 labeledcoefficients K11 to K33 are analog multipliers for multiplyingrespective coefficient values, and blocks 111 to 113 indicated by + signare analog adders. When a circuit of such a configuration is used,correct detected values Ax, Ay and Az are provided as output voltages ofthe adders 111 to 113. This is readily understood from the fact thatthis circuit corresponds to the above describe operational equation.

The circuit with respect to the three dimensional detector has beendescribed as above. With respect to the two dimensional detector, it issufficient that the operation expressed below can be performed:

Ax=K11Vx+K12Vy

Ay=K21Vx+K22Vy

Accordingly, a circuit shown, in a block form, in FIG. 12 may be usedfor this purpose. Blocks 201 to 204 are analog multipliers formultiplying respective coefficient values, and correct detected valuesAx and Ay are provided as output voltages from adders 211 and 212.

It is to be noted that nine coefficients are used in the case of thethree dimensional detector, and four coefficients are used in the twodimensional detector. In the case where the coefficient values are zero,any multiplier therefor becomes unnecessary.

An example of the actual circuit configuration of the multiplier and theadder shown, in a block form, in FIGS. 11 and 12 will now be described.FIG. 13 is a circuit diagram showing an example of the configuration ofthe multiplier. When a voltage Vin is applied to the input side of theoperational amplifier OP1, a voltage Vout is provided on the outputside. Here, when it is assumed that R3 is expressed as R3=R1//R2 (//indicates the resistance value when two resistors are connected inparallel), the following relationship holds:

Vout=−(R2/R1)·Vin

Accordingly, this operational amplifier functions as a multiplier formultiplying coefficient—(R2/R1). On the other hand, FIG. 14 is a circuitdiagram showing an example of the configuration of the adder. It issufficient to use resistors R all having the same resistance value. Whenvoltages Vin1, Vin2 and Vin3 are applied to the input side of theoperational amplifier OP2, a voltage Vout is provided on the outputside. Here, the voltage Vout is expressed as follows:

Vout=(Vin1+Vin2+Vin3)·⅔

Accordingly, addition of an input voltage can be carried out. A circuithaving both the multiplier and the adder is shown in FIG. 15. Whenvoltages Vin1, Vin2 and Vin3 are applied to the input side of theoperational amplifier OP3, a voltage Vout is provided on the outputside. Here, Vout is expressed as follows:

Vout=−((R4/R1)·Vin1

+(R4/R2)·Vin2

+(R4/R3)·Vin3)

Namely, this circuit performs a function doubling as a multiplier and anadder.

FIG. 16 is a diagram showing an actual circuit for performing anoperation expressed below by using the multiplier shown in FIG. 13 andthe adder shown in FIG. 14:

Ax=(K11Vx+K12Vy+K13Vz)·⅔

Here, an example of the circuit configuration in the case of K11>0,K12>0 and K13>0 is shown. Voltages Vx, Vy and Vz are voltages whenvoltages appearing on the voltage meters 61 to 63 of FIGS. 6a to 6 c areapplied as they are, respectively. These voltages are amplified by theoperational amplifiers OP4, OP5 and OP6 so that they are equal to values−K11 times, −K12 times and −K13 times larger than Vx, Vy and Vz,respectively. To realize this, it is sufficient that it is assumed thatthe relationships expressed as |R13|=R11//R12, |R23|=R21//R22, and|R33|=R31//R32 hold, and that respective resistance values are set sothat |K11|=R12/R11, |K12|=R22/R21 and |K13|=R32/R31 hold. By thisamplifying operation, sign is inverted. With respect to Vy, since K12<0,it is sufficient that the sign remains in an inverted state. Incontrast, with respect to Vx and Vz, since K11>0 and K13>0, it isnecessary to invert the sign for a second time to convert the sign tothe original one for a second time. In view of this, by operationalamplifiers OP7 and OP8, inversion of sign is carried out. Assuming nowthat R14=R15=2·R16 and R34=R35=2·R36 hold, the amplification factors ofthe operational amplifiers OP7 and OP8 are equal to 1 to serve as afunction to merely invert the sign. Thus, respective values of K11Vx,K12Vy and K13Vz are determined, and voltages corresponding to thesevalues are applied to the operational amplifier OP9. Here, when it isassumed that R41=R42=R43=R44=R45 holds, the operational amplifier OP9functions as an adder. Thus, an output voltage Vout expressed below isoutputted:

Vout=(K11Vx+K12Vy+K13Vz)·⅔

This output voltage Vout corresponds to a detected value Ax to bedetermined.

2.3 Other embodiments

An example of the signal processing circuit for force detector accordingto this invention has been described with reference to FIG. 16. Inaddition, this invention can be realized by using various circuits. Asthe multiplier and the adder in this invention, any circuit capable ofeffecting multiplication and addition by analog processing may be used.Further, it is not necessary to constitute the multiplier and the adderwith separate circuit elements, respectively. For example, if a circuitas shown in FIG. 15 is used, a single operational amplifier OP3 canserve as both the multiplier and the adder. This is advantageous in thatthe number of parts can be reduced. It is to be noted that, in the caseof utilizing this circuit, it is necessary to allow input voltages Vin1,Vin2 and Vin3 to have sign in consideration of the sign of thecoefficient K. Further, an approach may be employed to provide threeresistors to connect them in a Y form such that their one ends arecommonly connected to apply voltages to respective the other ends, thusto take out an output from the common terminal. Anyway, in the casewhere an approach is employed to perform corrective operation by such ananalog circuit, the cost can be lower than that in the case wherecorrective operation is carried out by the digital circuit, and theoperation is completed at a speed higher than that in the latter case.Accordingly, this is advantageous in the case where there is such anecessity to measure a momentary phenomenon. Particularly, in the caseof the acceleration detector, there is such a use to detect shock at thetime of collision. If this invention is applied to such a use, a correctmeasured value can be momentarily obtained. As stated above, the signalprocessing circuit according to this invention can be widely appliedmainly to a force detector, and further to an acceleration detector or amagnetic detector, etc. While the acceleration detector has beendescribed in the embodiment of this application, this invention can bewidely applied to a force detector or a magnetic detector.

2.4 Advantages with this processing circuit

As described above, in accordance with a processing circuit for anacceleration detector of this invention, an approach is employed todetermine in advance an inverse matrix of the characteristic matrixshowing how interference produced between compoments in respective axialdirections is to carry out corrective operation using this inversematrix by the analog operation circuit, thus making it possible tomomentarily provide correct measured values in which the influence ofinterference is canceled by using a low cost circuit.

§3 Test of the Sensor

3.1 Principle of a test method according to this invention

The method of mass producing acceleration sensors as shown in thepreviously described §1 is disclosed in the specification of the U.S.patent application Ser. No. 526,837 (European Patent Application No.90110066.9). Prior to shipping or forwarding such sensors as theproducts, it is necessary to conduct a test as to whether or not thereis any problem in the function as the acceleration sensor. As this testmethod, an approach may be employed to give vibration to thisacceleration sensor by means of a vibration generator to check an outputfrom the sensor at this time to thereby conduct a test. However, aspreviously described, the testing apparatus becomes large and only adynamic characteristic can be provided. Particularly, since this sensorcan detect an acceleration in all directions of X, Y and Z in the threedimensional coordinate system, it is necessary to give vibration inconsideration of directions of three dimensions. As a result, thetesting apparatus becomes considerably complicated.

In accordance with the testing method according to this invention, thesensor can be placed in the same environment where an acceleration isexerted without actually applying acceleration to the sensor. The basicprinciple is as follows. Initially, several electrode layers are formedat predetermined portions within the sensor. For this electrode layer,any layer comprised of a conductive material may be used. Actually, itis sufficient to form thin layers in metal such as aluminum atpredetermined portions by vacuum deposition or sputtering. In this case,it is preferable to coat the upper surface of the aluminum with SiO₂film or SiN film for protection of the surface. The electrode layers areformed at respective portions as described below. Initially, as shown inFIG. 4, an electrode layer E1 (indicated by hatching in the figure) isformed within the groove 31 provided in the control member 30, and, asshown in FIG. 5, an electrode layer E2 (indicated by hatching in thefigure) is formed in the groove 41 provided in the control member 40.Further, as shown in FIG. 17, an electrode layer E3 (indicated byhatching in the figure: although formed over five surfaces, this layeris a single electrode layer electrically conductive) is formed on theentire side surfaces and the bottom surface of the weight body 20, andelectrode layers E4 to E7 (indicated by hatching in the figure) areformed on respective inside surfaces of pedestals 21 to 24,respectively. Further, on the upper surface of the semiconductor pellet10, as shown in FIG. 18, an electrode layer E8 (indicated by hatching)is formed so as to avoid resistance elements R. In this way, in FIGS. 4,5, 17 and 18, electrode layers are formed in the hatched areas,respectively. As a result, the cross sectional view of the sensor centerportion within the package is as shown in FIG. 19 (In FIG. 19, thehatched portions indicate electrode layers, and hatchings indicating thecross section is omitted because the figure becomes intricate). By FIG.19, the relative positional relationship of respective electrode layersE1 to E8 can be understood. The wave lines in FIG. 19 indicate wiringswith respect to respective electrode layers. Such wirings can beconnected to the lead 52 for external wiring (refer to FIG. 1) outsidethe package by means of bonding wire. In addition, wiring is implementedto the electrode layer E3 formed on the weight body 20 by means ofbonding wires 25.

The feature of the respective electrode layers E1 to E8 formed in thisway is that they are formed at opposite positions every paired electrodelayers, respectively. Namely, as shown in FIG. 19, E2:E8, E3:E4, E3:E5,E3:E6, E3:E7, E3:E1 are formed at positions opposite to each other (fivesurfaces of the electrode layer E3 are opposite to different electrodelayers, respectively). When voltages are applied to electrodes oppositein this way, respectively, coulomb forces are exerted between therespective both electrode layers. Namely, when voltages of the samepolarity are applied to the both electrode layers, a repulsive force isexerted, while when voltages of different polarities are appliedthereto, an attractive force is exerted. When a voltage is now assumedto be applied so that a repulsive force is exerted between E3 and E4 andan attractive force is exerted between E3 and E5, there takes place thesame phenomenon as that where a force in the X direction is exerted onthe weight body 20. In other words, this sensor can be placed under thesame environment as that where an acceleration in the −X direction isexerted on the sensor body (when an acceleration is exerted on thesensor body, an inertia force in a direction opposite to the above isexerted on the weight body). Under this environment, whether or not anoutput corresponding to changes in the resistance values of theresistance elements, which indicates an acceleration in the −Xdirection, is detected is examined, thereby making it possible toconduct a test with respect to the acceleration in the −X direction. Ifan attractive force and a repulsive force are exerted in an oppositemanner, a test with respect to the acceleration in the +X direction canbe conducted. Exactly in the same manner, if voltages are applied sothat an attractive force is exerted between E3 and E6, and a repulsiveforce is exerted between E3 and E7, a test with respect to theacceleration in the Y direction (upper direction perpendicular to planesurface of paper of FIG. 19) can be conducted. If an attractive forceand a repulsive force are exerted in an opposite manner, a test withrespect to the acceleration in the +Y direction (lower directionperpendicular to plane surface of paper of FIG. 19) can be conducted.Further, if voltages are applies so that an attractive force is exertedbetween E2 and E8, and a repulsive force is exerted between E3 and E1, atest with respect to the acceleration in the −Z direction can beconducted. If an attractive force and a repulsive force are exerted inan opposite manner, a test with respect to the acceleration in the +Zdirection can be conducted. As previously described, since respectiveelectrode layers and respective resistance elements for detection ofacceleration are both electrically connected to leads 52 (refer toFIG. 1) outside the package by means of bonding wires, the abovedescribed test can be conducted by an operation to only monitor anacceleration detected signal outputted from a predetermined leadterminal while simply applying a predetermined voltage to thepredetermined lead terminal. As stated above, in accordance with thetesting method according to this invention, it is possible to carry outan acceleration detecting test with respect to all directions of threedimensions extremely with ease.

3.2 More practical embodiment

With respect to embodiment shown in FIG. 19, it is necessary to formelectrode layers at considerably large number of portions. Accordingly,this embodiment is not so practical. It is preferable to carry out anacceleration detecting test with respect to all directions of threedimensions by electrode layers provided at necessary and minimumportions if possible. Let now suppose the following model. FIG. 20 is across sectional view of the center portion of the acceleration sensor.Points P1 and P2 are taken at two portions on the semiconductor pellet10, and points Q1 and Q2 are taken at two portions inside the controlmember 40. In this case, the points P1 and Q1 are opposite to eachother, and the points P2 and Q2 are opposite to each other. When it isnow assumed that an attractive force is exerted between the points P1and Q1, and a repulsive force is exerted between the points P2 and Q2,the points P1 and p2 are subjected to displacement relative to thepoints Q1 and Q2. As a result, as shown in FIG. 21, the semiconductorpellet 10 produces a mechanical deformation. This state is the samestate where a force Fx in the +X direction is exerted on the weight body20. In other words, this state is the same state where an accelerationin the −X direction is exerted on the sensor body. Further, if anattractive force and a repulsive force are exerted in an oppositemanner, there results the same state as the state where an accelerationin the +X direction is exerted. Thus, it is seen that if electrodelayers are formed at predetermined portions on the upper surface of thesemiconductor pellet 10 and at predetermined portions on the lowersurface of the control member 40, an acceleration detecting test in the±X direction can be conducted. An acceleration detecting test in the ±Ydirection can be similarly carried out by varying the positions ofelectrode layers by an angle of 90 degrees. When a repulsive force isexerted between the points P1 and Q1 and a repulsive force is alsoexerted between the points P2 and Q2, there results the same state asthe state where a force Fz in the Z direction is exerted on the weightbody 20 as shown in FIG. 22. In other words, there results the samestate as the state where an acceleration in the +Z direction is exertedon the sensor body. Further, if an attractive force is exerted bothbetween the points P1 and Q1 and between the points P2 and Q2, thereresults the same state as the state where an acceleration in the −Zdirection is exerted. Thus, it is seen that electrode layers are formedat predetermined portions on the upper surface of the semiconductorpellet 10 and at predetermined portions on the lower surface of thecontrol member 40, thereby making it possible to conduct an accelerationdetecting test in the ±Z direction.

As stated above, eventually, if electrode layers are formed atpredetermined portions on the upper surface of the semiconductor pellet10 and at predetermined portions on the lower surface of the controlmember 40, it is possible to carry out an acceleration detecting testwith respect to all directions of three dimensions. A further practicalexample of the electrode layer arrangement will now be described.Initially, on the upper surface of the semiconductor pellet 10, asindicated by hatching (which does not indicate the cross section) inFIG. 23, four electrode layers E9 to E12 are formed. Respectiveelectrode layers are formed so as to avoid the areas where resistorelements R are formed, and are connected to bonding pads B9 to B12 bymeans of wiring layers W9 to W12, respectively. Bonding wires (notshown) are connected to bonding pads B9 to B12, and electricalconnections with respect to leads outside the package are finallyimplemented. Although not shown in FIG. 23, the resistance elements Rare also connected to the bonding pads 14, respectively, and areelectrically connected to leads outside the package. On thesemiconductor pellet 10, wiring layers such as aluminum, etc. are formedin order to carry out wirings with respect to resistance elements R. Inthis case, for forming electrode layers E9 to E12 or wiring layers W9 toW12, it is preferable to use the same mask as that for the wiring layerssuch as aluminum, etc. Thus, by only adding the work for altering theconventional mask pattern, it is possible to form additional electrodelayers E9 to E12 or wiring layers W9 to W12 for test. Of course,electrode layers E9 to E12 or wiring layers W9 to W12 may be formed as adiffused layer by making use of the diffusion process for forming gaugeresistors, etc. The manufacturing process for the semiconductor pellet10 can employ exactly the same process as that of the prior art. On theother hand, the electrode layer E2 shown in FIG. 5 may be formed on thelower surface of the control member 40. This may be accomplished byallowing aluminum, etc. to adhere on the surface by vacuum deposition orsputtering. While the electrode layer E2 shown in FIG. 5 is formed as aphysically single electrode layer, an approach may be of course employedto allow this electrode layer E2 to be comprised of physically pluralelectrodes to electrically connect these electrodes so that they havethe same potential, thus to constitute this electrode layer with“electrode layer which is divided into a plurality of electrode sectionsfrom a physical point of view, but is formed as a single electrode layerfrom an electric point of view”. The cross sectional view when electrodelayers as described above are formed is shown in FIG. 24. Wiringindicated by the wave lines in the figure is implemented to theelectrode layer E2, and is further connected to external leads. In thisway, a single electrode layer E2 is formed as one electrode layer, andfour subelectrode layers E9 to E12 are formed as the other electrodelayers opposite to the single electrode layer.

To conduct a test for such an acceleration sensor, by employing thefollowing approach under the state where a voltage of +V is applied tothe electrode layer E2, an acceleration detecting test with respect toall directions of three dimensions can be conducted.

(1) If +V and −V are applied to E10 and E12, respectively, a force +Fxcan be exerted on the weight body 20. Thus, an acceleration detectingtest in the −X direction can be carried out.

(2) If −V and +V are applied to E10 and E12, respectively, a force −Fxcan be exerted on the weight body 20. Thus, an acceleration detectingtest in the +X direction can be carried out.

(3) If +V and −V are applied to E11 and E9, respectively, a force +Fycan be exerted on the weight body 20. Thus, an acceleration detectingtest in the −Y direction can be carried out.

(4) If −V and +V are applied to E11 and E9, respectively, a force −Fycan be exerted on the weight body 20. Thus, an acceleration detectingtest in the +Y direction can be carried out.

(5) If −V is applied to each of E9 to E12, a force +Fz can be exerted onthe weight body 20. Thus, an acceleration detecting test in the −Zdirection can be carried out.

(6) If +V is applied to each of E9 to E12, a force −Fz can be exerted onthe weight body 20. Thus, an acceleration detecting test in the +Zdirection can be carried out.

While the acceleration detecting test on the X, Y and Z axes has beendescribed above, the detecting test for an acceleration in a directionnot on the X, Y and Z axes may be also carried out by applyingpredetermined voltages to the electrode layers E9 to E12, respectively.

It is to be noted that applied voltages +V and −V should be set to avoltage value such that changes in the resistance values of the resistorelements R can be sufficiently detected. This value depends upon thethickness and the diameter of the flexible portion 12 forming an annulardiaphragm.

3.3 Other embodiments

The above-described embodiment should be considered to be one mode ofthis invention. In addition to this, various embodiments areconceivable. Several ones thereof will be described below. In theembodiment in which the cross section is shown in FIG. 25, an electrodelayer E13 is formed in place of the electrode layer E2. Since theelectrode layer E13 is formed on the upper surface of the control member40, wiring to the external is facilitated. It is to be noted that acoulomb force exerted between electrodes becomes weaker to some extentthan that of the previously described embodiment.

In the embodiment shown in FIG. 26, electrode layers E14 to E17(indicated by hatching) are formed in place of the electrode layers E9to E12 of the above-described embodiment, and wiring layers W14 to W17and bonding pads B14 to B17 for the electrode layers E14 to E17 areformed. Such an arrangement is advantageous in that there is littlepossibility that wiring layers give obstruction to wirings forresistance elements R. However, since electrode layers are arrangedinside of the position where the semiconductor pellet 10 has thegreatest flexibility, and the area of the electrode is reduced, theacting efficiency of force is lowered.

In the embodiment shown in FIGS. 27 and 28, the arrangement relationshipin a longitudinal direction of electrode layers is opposite to that ofthe previously described embodiment. Namely, four electrode layers E18to E21 (indicated by hatching) and wiring layers W18 to W21 therefor areformed within a groove 41 on the lower surface of the control member 40.As the electrode opposite thereto, e.g., a single electrode E8 formed onthe semiconductor pellet 10 as shown in FIG. 18 may be employed.

In the embodiment shown in FIG. 29, four electrode layers E18′ to E21′are formed in place of the electrode layer E8 of the embodiment shown inFIG. 28. These electrode layers E18′ to E21′ are symmetrical toelectrodes E18 to E21, and four sets of electrode pairs opposite in alongitudinal direction are formed. If four sets of (eight in total) areall caused to be electrically independent, various voltages are appliedto these electrodes, thereby making it possible to conduct a test withrespect to various directions. For example, as shown in FIG. 29, ifcharges “++” and “−−” are given to electrodes E19 and E19′,respectively, and, at the same time, charges “++++” and “−−−−” are givento electrodes E21 and E21′, respectively (the number of + or − indicatesthe quantity of charges), while an attractive force is between all upperand lower electrode pairs, since an attractive force between electrodepairs on the right side in the figure becomes large, a test in the samestate as the state where Fxz (resultant force of Fx and Fz) in adirection as shown in the figure is exerted can be conducted.

In addition, various embodiments are conceivable. In short, as long asthere is employed an arrangement adapted to permit a coulomb force to beexerted between a first portion to produce a displacement by the actionof a force and a second portion present at the position opposite to thefirst portion, any arrangement may be employed in this invention.

While the above described embodiments are all directed to theacceleration sensor, this invention can be applied, exactly in the samemanner, to a magnetic sensor using a magnetic body in place of a weightbody, or to a force sensor. Further, this invention is applicable notonly to a three dimensional sensor, but also to a two dimensional or onedimensional sensor. For example, in the case of a two dimensional sensorfor detecting acceleration or magnetism in the X and Z-axes, or a onedimensional sensor for detecting acceleration or magnetism in the X-axisdirection, it is sufficient to provide only two electrodes of E10 andE12 of four electrodes E9 to E12 shown in FIG. 23.

3.4 Method of applying voltage

Finally, an example of a method of applying a voltage for carrying outthis testing method is shown. FIG. 30a is a model view showing a methodof applying a voltage for realizing the same state as the state where aforce in a Z direction is exerted on a weight body (not shown).Electrode E22 on the control unit 40 side and electrodes E23 and E24 onthe semiconductor pellet 10 side are caused to produce charges ofporalities opposite to each other by means of power supply V, thusallowing an attractive force to be exerted therebetween.

On the other hand, FIG. 30b is a model view showing a method of applyinga voltage for realizing the same state as the state where a force in the−Z direction is exerted on the weight body. Electrode E22 on the controlmember 40 and electrodes E23 and E24 on the semiconductor pellet 10 arecaused to produce charges of the same polarity by means of power supplyV, thus allowing a repulsive force to be exerted therebetween. In thisembodiment, with a view to carrying out a more efficient voltageapplication, there is an arrangement in which a different electrode E25is formed on the upper surface of the control member 40, thus to givepositive charges to the electrode E25. Namely, by allowing the controlmember 40 to be in the state of polarization on the opposite surfacesthereof, the electrode E22 is caused to produce negative charges.Further, positive charges are given to the body of the semiconductorpellet 10. Since an insulating layer 10 a (generally, SiO₂ film or SiNfilm) is formed as shown on the upper surface of the semiconductorpellet 10, the insulating layer 10 a is allowed to be in the state ofpolarization on the opposite surfaces thereof, thereby causingelectrodes E23 and E24 to produce negative charges.

3.5 Advantages with this testing method

(1) Since a coulomb force is exerted between a first portion and asecond portion opposite thereto to allow the strain generative body toinduce a mechanical deformation, thus to create the same state as thestate where an external force is exerted on the working body, it ispossible to conduct a test for a sensor without actually exerting anexternal force.

(2) Since a voltage of a predetermine polarity is applied acrossopposite two electrode layers to thereby exert a coulomb forcetherebetween, a test having a higher degree of freedom can be conducted.

(3) If one electrode layer is caused to be formed as a single electrodelayer and the other electrode layer is caused to be formed as aplurality of subelectrode layers, selection of polarities of appliedvoltages is made, thereby making it possible to conduct a test in whicha coulomb force is exerted in various directions.

(4) Since electrode layers for carrying out the above described test areformed within the acceleration sensor to implement wiring thereto, atest can be carried out simply by connecting a predetermined electriccircuit to the acceleration sensor.

(5) Since electrode layers for carrying out the above described test areformed within the magnetic sensor to implement wiring thereto, a testcan be carried out simply by connecting a predetermined electric circuitto the magnetic sensor.

(6) Since, in the above described acceleration or magnetic sensor, oneelectrode layer is constituted with a single electrode layer and theother electrode layer is constituted with a plurality of subelectrodelayers, selection of polarities of applied voltages is made, therebymaking it possible to conduct a test in which a coulomb force is exertedin various directions.

(7) Since two subelectrodes are provided in the above describedacceleration or magnetic sensor, a test in which a coulomb force isexerted with respect to two directions perpendicular to each other canbe carried out.

(8) Since four subelectrode layers are provided in a crossing form inthe above described acceleration or magnetic sensor, a test in which acoulomb force is exerted with respect to three directions perpendicularto each other can be carried out.

§4 Sensor Suitable for High Sensitivity Measurement

4.1 Structure of the sensor

FIG. 31 is a structural cross sectional view of an acceleration sensorsuitable for high sensitivity measurement according to an embodiment ofthis invention. The sensor center section 300 is composed of fourelements of a semiconductor pellet 310, a weight body 320, a pedestal330, and a control substrate 340. This sensor center section isconnected to the bottom surface inside a package 400. A cover 410 isfitted over the upper part of the package 400. Further, leads 420 aredrawn out from the side portions of the packagte 400 to the external.FIG. 32 is a perspective view of the sensor center section. A pluralityof resistance elements R are formed on the upper surface of thesemiconductor pellet 310, and respective resistance elements R areelectrically connected to bonding pads 352. Bonding pads 352 and leads420 are connected by means of bonding wires 351.

FIG. 33 is a detailed cross sectional view of the sensor center sectionof the acceleration sensor shown in FIG. 31. In this embodiment, thesemiconductor pellet 310 is comprised of a single crystal siliconsubstrate, and resistance elements R are formed by diffusing impurityinto the portion on the side of the upper surface of the semiconductorpellet 310. Of course, ion implantation process may be used, or theremay be employed SOI structure in which gauge resistors are stacked on asilicon substrate. The resistance elements formed in this way have thepiezo resistive effect. Namely, such elements have the property in whichthe electric resistance varies on the basis of a mechanical deformation.On the side of the lower surface of the semiconductor pellet 310,annular groove portions C1 are formed. In this embodiment, the grooveportion C1 employs a taper structure such that the width become narroweraccording as the distance up to the bottom becomes small. However, agroove having the same width up to the bottom may be employed. FIG. 34is a top view of the semiconductor pellet 310. The groove portion C1 dugon the lower surface is indicated by broken lines. Assuming now thatcoordinate axes X, Y and Z as indicated by arrow are defined, the crosssection along the X-axis of the semiconductor pellet shown in FIG. 34 isshown in FIG. 33. By the formation of this groove portion C1, thesemiconductor pellet 310 can be divided into three portions. Namely,there are three portions of a working portion 311 positioned inside thegroove portion C1, a flexible portion 312 positioned just above thegroove portion C1, and a fixed portion 313 positioned outside the grooveportion C1. In other words, the working portion 311 is positioned at thecentral portion of the semiconductor pellet 310, the flexible portion312 is positioned around the working portion 311, and the fixed portion313 is positioned around the flexible portion 312. The flexible portion312 has a thickness thinner than those of other portions by the presenceof the groove portion C1. For this reason, the flexible portion 312 hasflexibility. In place of forming such an groove, through holes may bepartially formed through the substrate to allow it to have flexibility.

A weight body 320 is connected to the lower surface of the workingportion 311, and a pedestal 330 is connected to the lower surface of thefixed portion 313. FIG. 35 is a top view of the weight body 310 and thepedestal 330. The cross section along the cutting plane line 33—33 ofFIG. 35 is shown in FIG. 33. There is a difference in level on the uppersurface of the weight body 320. That is, a weight body upper surfacecentral portion 321 and a weight body upper surface peripheral portion322 are formed. The weight body upper surface central portion 321 is aportion slightly raised at the central portion of the upper surface ofthe weight body 320. This portion is connected to the lower portion ofthe working portion 311. Accordingly, a gap portion C2 is formed betweenthe weight body upper surface peripheral portion 322 and the lowersurface of the semiconductor pellet 310. The pedestal 330 is comprisedof eight members arranged in eight directions around the weight body320. Between the weight body 320 and the pedestal 330, a groove portionC3 and a groove portion C4 are formed. As described later, the weightbody 320 and the pedestal 330 are members originally comprised of thesame substrate. These members are separated by cutting through thegroove portions C3 and C4. As shown in FIG. 35, the groove portion C3has a width L1, and the groove portion C4 has a width L2 narrower thanthe groove portion C3. As is clear from FIG. 33, the groove portions C3and C4 are formed at the upper and lower parts, respectively. Of course,L1 may be equal to L2 from the requirement of machining.

The control substrate 340 is connected to the lower surface of thepedestal 330. The top view of the control substrate 340 is shown in FIG.36. A groove portion C5 is dug in the control substrate 340 leaving theperipheral portion thereof. The bottom surface of the groove portion C5forms a control surface 341. The cross section along the cutting planeline 33—33 of FIG. 36 is shown in FIG. 33. As shown in FIG. 33, only theperipheral portion of the control substrate is connected to the lowersurface of the pedestal 330.

4.2 Method of manufacturing the sensor

For helping understanding of the structure of the sensor center section300, the manufacturing method thereof will be briefly described.Initially, a semiconductor pellet 310 as shown in FIG. 34 is prepared.Here, the groove portion C1 may be formed by, e.g., etching process, andresistance elements R may be formed by an impurity injection processusing a predetermined mask. An auxiliary substrate 350 of which crosssectional view and top view are respectively shown in FIGS. 37 and 38 isprepared. Here, the cross section along the cutting plane line 37—37 ofFIG. 38 corresponds to FIG. 37. As the material of the auxiliarysubstrate 350, it is preferable to use silicon which is the samematerial as that of the semiconductor pellet 310, or glass. This isbecause since the semiconductor pellet 310 and the auxiliary substrate350 are connected later, the both coefficients of thermal expansion arecaused to be equal to each other to thereby suppress occurrence ofcracks, thus to improve the temperature characteristic. On the side ofthe upper surface of the auxiliary substrate 350, a groove portion C3 inthe form of parallel crosses is dug. Inside the groove portion C3, a gapportion C2 having a width L3 is formed. As a result, there occurs adifference in level between the weight body upper surface centralportion 321 and the weight body upper surface peripheral portion 322.The gap portion C2 may be formed by, e.g., etching process, and thegroove portion C3 may be formed by the cutting process using a dicingblade. It should be noted that the groove portion C4 shown in FIG. 33 or35 is not yet formed. Accordingly, the auxiliary substrate 350 is in thestate of a single substrate. The lower surface of the auxiliarysubstrate 350 prepared in this way is connected to the lower surface ofthe semiconductor pellet 310. At this time, the weight body uppersurface central portion 321 is connected to the lower surface of theworking portion 311, and the portion around the auxiliary substrate 350(the portion which will constitute the pedestal 330 later) is connectedto the fixed portion 313 lower surface. After such a connection iscompleted, the lower surface of the auxiliary substrate 350 is subjectedto cutting process by means of a dicing blade having a width L2, thus toform a groove portion C4. The groove portion C3 and the groove portionC4 communicate with eath other, and the auxiliary substrate 350 isdivided into the weight body 320 at the central portion and the pedestal330 at the peripheral portion. Thereafter, a control substrate 340 asshown in FIG. 36 is prepared to form a groove portion C5 by the etchingprocess, etc. The control substrate 340 thus processed is connected tothe lower surface of the pedestal 330. After undergoing theabove-described manufacturing process steps, sensor center portion 300shown in FIG. 33 is provided.

It is to be noted that the above-described process is directed to amethod of manufacturing a single unit, but actually manufacturing isconducted every wafer in the state where a plurality of such units arelongitudinally and breadthly arranged. Namely, a wafer on which unitsshown in FIG. 34 are longitudinally and breadthly arranged and anauxiliary substrate on which units shown in FIG. 35 are longitudinallyand breadthly arranged are connected. To this assembly, an auxiliarysubstrate on which units shown in FIG. 36 are longitudinally andbreadthly arranged is further connected. Thereafter, the assembly thusobtained is finally cut every respective units. It is to be noted thatwhile the gap portion C2 is formed on the auxiliary substrate 350 sidein this example, the fixed portion of the semiconductor pellet 310 maybe etched to provide the gap portion C2 on the semiconductor pellet 310side.

4.3 Operation of the sensor

The operation of this sensor will now be described. As shown in FIG. 31,the sensor center portion 300 is fixed to the bottom surface at theinside of the package 400. Since the control substrate 340, the pedestal330 and the fixed portion 313 are in the state where they are fixed toeach other, the fixed portion 313 is indirectly fixed to the package400. On the other hand, the weight body 320 is in a hanging state withina space peripheraly encompassed by the pedestal 330. Namely, as shown inFIG. 33, the groove portion C5 is formed on the side of the lowersurface of the weight body 320, the groove portions C3 and C4 are formedon the side of the side surface thereof, and the gap portion C2 isformed on the side of the peripheral portion of the upper surfacethereof. Further, only the central portion of the upper surface of theweight body 320 is connected to the working portion 311. When anacceleration is exerted on the weight body 320 placed in such a hangingstate, a force is exerted on the working portion 311 by thisacceleration. As previously described, since the flexible portion 312 isthe portion having flexibility, when a force is exerted on the workingportion 311, the flexible portion 312 produces a bend. As a result, theworking portion 311 produces a displacement relative to the fixedportion 313. The bend of the flexible portion 312 causes mechanicaldeformations in the resistance elements R, so there occur changes in theelectric resistance values of the resistance elements R. Since changesin the electric resistance values can be detected outside the sensor bymaking use of bonding wires 351 and leads 420 as shown in FIG. 32. Inthe case of the sensor of this embodiment, by arranging resistanceelements R at positions as shown in FIG. 34, it is possible toindependently detect acceleration components in respective axialdirections of X, Y and Z. The principle of detection has been alreadydescribed in §1.

4.4 Feature of the sensor

The feature of the acceleration sensor which has been described above isthat it is suitable for high sensitivity acceleration measurement. Thefirst reason is that the volume of the weight body 320 can be as largeas possible within a limited space. As shown in FIG. 33, the weight body320 is connected only at the weight body upper surface central portion321 to the working portion 311, but the peripheral thereof is laterallywidened to extend up to the inside portion of the fixed portion 313striding over the groove portion C1. For this reason, the mass of theweight body can be increased. As a result, even if a small accelerationis applied, this sensor can transmit a sufficient force to the workingportion 311. The second reason is that the control member for allowing adisplacement of the weight body to limitatively fall within apredetermined range can be constituted with a simple structure. In thestructure shown in FIG. 33, a displacement in an upper direction of theweight body 320, a displacement in a lower lateral direction thereof,and a displacement in a lower direction thereof are caused to alllimitatively fall within a predetermined ranges, respectively. First,with respect to a displacement in an upper direction, it can beunderstood that a portion of the lower surface of the fixed portion 313functions as a control member. In FIG. 33, when the weight body 320attempts to move in an upper direction, the working portion 311 moves inan upper direction by bend of the flexible portion 312. Following this,the weight body upper surfaces central portion 321 also moves in anupper direction. However, the outer circumferential portion of theweight body upper surface peripheral portion 322 comes into contact withthe lower surface of the fixed portion 313, so movement thereof isprevented. In other words, a displacement in an upper direction of theweight body 320 is allowed to limitatively fall within a range of thesize of the gap portion C2. This limiting action is made more clear whenreference is made to FIG. 39. FIG. 39 is the bottom view of thesemiconductor pellet 310 wherein the position of the weight body 320 isindicated by broken lines. The weight body 320 is connected only to thehatched portion by slanting lines at the central portion (lower surfaceof the working portion 311). The portion outside the groove portion C1serves as the fixed portion 313. The portion of the hatched portion bydots of the portion outside the groove portion C1 is a surfaceperforming the function as the control member. The weight body 320 comesinto contact with this surface, so upward movement thereof is limited.On the other hand, with respect to movement in a lateral direction, asis clear from FIG. 33, the side surface of the weight body 320 comesinto contact with the inside surface of the pediestal 330. Thus,displacement is allowed to limitatively fall within a range of the sizeof the groove portion C4. Further, with respect to a displacement in alower direction, the lower surface of the weight body 320 comes intocontact with the control surface 341 of the control substrate 340. Thus,displacement is allowed to limitatively fall within a range of the sizeof the groove portion C5. Since displacement of the weight body 320 isallowed to limitatively fall within a predetermined range with respectto movement in all directions, the risk that the semiconductor pellet310 may be broken by an excessive displacement can be avoided. Such acontrol of displacement is particularly important in the case of a highsensitivity sensor. In accordance with the structure of this invention,since an approach is empolyed to control a displacement in an upperdirection by making use of the semiconductor pellet 310, and to controla displacement in a lateral direction by making use of the pedestal 330,there is no necessity of individually providing control members,respectively. As a result, the structure becomes very simple.Accordingly, massproduction can be advantageously carried out.

4.5 Other embodiments

While this invention has been described in connection with theembodiment shown, this invention is not limited only to this embodiment,but can be carried out in various forms. Several other embodiments areshown below.

As the method of forming the auxiliary substrate 350 shown in FIGS. 37and 38, the method of forming the groove portion C3 by cutting processusing a dicing blade, and forming the groove portion C2 by etchingprocess is shown as an example in the previously described embodiment.In addition, the gap portion C2 may be formed by cutting process using adicing blade. This is accomplished by preparing a dicing blade 361having a width L3, as shown in FIG. 40, for example, to carry outcutting process so as to allow it to pass through a route indicated bybroken lines in FIG. 41 to form an auxiliary substrate 350′. Of course,an approach may be employed to allow dicing blade having a less than thewidth L3 to pass several times to dig a groove having the width L3. InFIG. 41, only the hatched area is the portion which does not undergocutting process. When such a cutting process is carried out, the portionserving as the pedestal 330 is partially cut. However, any trouble doesnot occur with respect to the function as the pedestal 330. Generally,in the case of mass producing auxiliary substrates, auxiliary substrate350′ as shown in FIG. 41 is assumed as a unit to arrange a large ofauxiliary substrates longitudinally and breadthly on a wafer to carryout process of the substrates every wafer thereafter to cut respectiveunits by the dicing process. For such a process every wafer, the abovedescribed cutting process is very efficient. When an approach isemployed to linearly move the dicing blade 361 on a wafer, cuttingprocess for a large number of auxiliary substrates can be carried out ata time.

In the previously described embodiment, the groove portion C1 dug in thesemiconductor pellet 310 was annular as shown in FIG. 34. Such anannular groove can be easily formed by the etching process. However, ifan attempt is made to form such an annular groove by the cutting processusing a dicing blade, the movement control of the dicing blade becomescomplicated. This is not suitable. In this invention, the groove portionformed in the semiconductor pellet 310 is not limited to the annulargroove portion. Here, the cross sectional view of the embodiment wherethe groove portion in the form of parallel crosses is formed on the sideof the lower surface of the semiconductor pellet 310′ is shown in FIG.42, and the bottom view thereof is shown in FIG. 43. Such a groove maybe provided by preparing a dicing blade 362 having a width L4 as shownin FIG. 43 to allow it to pass through a route indicated by broken linesto carry out cutting process. Of course, an approach may be employed toallow a dicing blade having a less than the width L4 to pass severaltimes to dig a groove having a width L4. Only the hatched area in FIG.43 is the portion which does not undergo cutting process. When such acutting process is carried out, the shapes of the working portion 311′,the flexible portion 312′ and the fixed portion 313′ are different tosome extent from those of the previously described embodiment, but theredoes not occur any inconvenience with respect to the functions ofrespective portions. FIG. 44 is a bottom view of this semiconductorpellet 310′ wherein the position of the weight body 320 is indicated bybroken lines. The weight body 320 is connected to only the hatchedportion by slanting lines at the central portion (the lower surface ofthe working portion 311′). The portion outside the groove portion C6serves as the fixed portion 313′. The hatched portion by dots of theportion outside the groove portion C6 serves as the surface performingthe function as the control member. This embodiment is also suitable fora method processing every wafer.

In the embodiment shown in FIG. 45, a spacer 370 is used in place of thecontrol substrate 340. For this spacer 370, e.g., a film of glass fiber,etc. may be used. When the spacer 370 is put between the lower surfaceof the pedestal 330 and the bottom surface at the inside of the package400, and is fixed therebetween by a method such as die bond, the bottomsurface itself at the inside of the package 400 can be utilized as amember for controlling a displacement in a lower direction of the weightbody 320. The allowed displacement in lower direction of the weight body320 is determined by the thickness of the spacer 370. In addition, inplace of using the spacer 370, an approach may be employed to etch thelower surface of the weight body 320 (the surface against the bottomsurfaces side of the package 400) to allow the weight body 320 to be ina floating state when the pedestal is connected to the package.Alternatively, an approach may be employed to dig a groove on the sideof the bottom surface at the inside of the package 400 to allow theweight body 320 to be in a floating state.

While this invention is applied to the acceleration sensor in the abovedescribed all embodiments, if the previously described weight body 320is replaced by a general working body, this invention is applicable to amagnetic sensor or a force sensor. For example, in the case where thisinvention is applied to the magnetic sensor, any working body responsiveto magnetism (magnetic body suits for this purpose) may be used insteadof the weight body 320. Further, in the case where this sensor isapplied to a force sensor, if an approach is employed to support thesemiconductor pellet 310 by the supporting member 380, as shown in FIG.46, for example, an external force F exerted as shown on the workingbody 320′ can be detected. Alternatively, if an approach is employed tosupport the semiconductor pellet 310 and the pedestal 330 by thesupporting member 390 as shown in FIG. 47, the same effect as the abovewill be provided.

4.6 Examples of utilization of the acceleration sensor

As described above, if this invention is applied to the accelerationsensor, it is possible to detect, with high sensitivity, an accelerationin three dimensional directions. Such a high sensitivity accelerationsensor can be utilized in various fields. For example, as the system forprotecting a passenger from an automotive vehicle accident, air bagsbeings becoming popular. However, since only acceleration sensors in onedimensional direction is put into practice for the time being, thepresent air bags are the system in which the front collision is assumed.Namely, as shown in FIG. 48, when an impact in a direction indicated byan arrow is detected, an air bag 510 is caused to be swollen in front ofa passenger 500 to protect the passenger 500 in a manner to put thepassenger between a seat 505 and the air bag 510. Accordingly, an airbag in a spherical form is used as the air bag 510. On the contrary,since a sensor according to this invention can detect, with highsensitivity, an acceleration in a three-dimensional direction, even inthe case where a side collision takes place, this sensor can detect animpact. Accordingly, as shown in FIG. 49, if an air bag 520 in a form tocover the side parts of the passenger 500 is prepared to swell this airbag in response to a detection signal from the acceleration sensoraccording to this invention, an air bag system capable of coping with aside collision can be introduced.

4.7 Detection sensitivity in respective axial directions of threedimensions

The sensor of this invention can detect force, acceleration andmagnetism in three dimensional directions. However, if there is a greatdifference between detection sensitivities of these physical quantitieswith respect to respective axial directions, this is a problem. Now letsuppose a simple model of an acceleration sensor as shown in FIG. 50.This acceleration sensor detects an acceleration applied to the weightbody 320 as a force (or moment) exerted on the point P on the uppersurface of the semiconductor pellet 310 (the foot of the perpendicularfrom the center of gravity G of the weight body 320 onto the uppersurface of the semiconductor pellet 320). Here, let define an X-axis, aY-axis (direction perpendicular to the plane surface of paper), and a Zaxis in directions indicated by arrows in FIG. 50, and assume anacceleration exerted on the weight body 320 of the mass m as anacceleration exerted on the center of gravity G. Thus, an accelerationin a Z-axis direction exerted on the center of gravity G is detected asa force Fz (=m·αz) exerted in a Z-axis direction at the point P. On thecontrary, an acceleration αx in an X-axis direction exerted on thecenter of gravity G is detected as a moment My (=m·αx·L) about theY-axis at the point P, and an acceleration αy in a Y-axis directionexerted on the center of gravity G is detected as a moment Mx (=m·αy·L)about the X-axis at the point P. Accordingly, if the semiconductorpellet 310 is of a structure symmetric in plane, a detection sensitivityof an acceleration exerted in an X-axis direction and a detectionsensitivity of an acceleration exerted in a Y-axis direction can benearly equal to each other. However, these detection sensitivities andthe detection sensitivity of an acceleration exerted in a Z-axisdirection are generally different.

The inventor of this application has drawn attention to the fact thatmoments Mx and My are quantities having the length L of theperpendicular as a parameter. The inventor notices that the detectionsensitivities in three axial directions of X, Y and Z can besubstantially equal to each other by determining L as a suitable value.As the result of the experiment, if L satisfies the following condition,the inventor has found out that detection sensitivities in three axialdirections are substantially equal to each other. Namely, as shown inFIG. 50, when the distance from the point P up to the inside portion ofthe groove depth portion dug in the semiconductor pellet 310 is assumedas r1, and the distance from the point P up to the outside portion ofthe groove depth portion is assumed as r2, if setting is made such thatthe relationship expressed as r1<L<r2 holds, detection sensitivities inthree axial directions are substantially equal to each other. It is tobe noted that the sensitivities of respective axes of X, Y and Z underchanges to some extent in dependency upon the form of the flexibleportion or the working portion, etc. as well. For this reason, there areinstance where the relationship expressed as r1<L is not completelysatisfied. As long as at least the relationship expressed as L<r2 ismaintained, the effect to equalize the detection sensitivities isexhibited. Accordingly, in the case of actually manufacturing the sensoraccording to this invention, it is preferable to design dimensions ofrespective portions in consideration of such a condition.

4.8 Method of testing sensor

In the case of mass producing sensors according to this invention, thereoccurs the necessity of testing respective sensors prior to shipping orforwarding. The method for easily carrying out such a test has beendescribed in §3. FIG. 51 is a side cross sectional view showing thestructure when this testing method is applied to the sensor centersection 300 shown in FIG. 33, and FIG. 52 is a top view of the controlsubstrate 340 at this time (the hatched portion indicates theelectrode). A single electrode plate E30 is formed on the bottom surfaceof the weight body 320, and four electrode plates E31 to E34 are formedso as to face the electrode plate E30 on the control surface 341 of thecontrol substrate 340. Wiring layers are connected to the electrodeplates, respectively, but an indication thereof is omitted here. If anapproach is employed to form such electrode layers to apply voltages ofpredetermined polarities to respective electrode layers, a coulomb forceis exerted between opposite electrode layers, thus making it possible toexert a force on the weight body 320 although no acceleration isexerted. By varying polarities of voltages applied to respectiveelectrode layers, it is possible to apply a force in various directions.By comparing voltages applied to respective electrode layers and aprimary sensor output, the test as to whether or not this sensornormally operates can be conducted.

4.9 Advantages with this sensor

(1) In accordance with the above described sensor, since there isemployed an arrangement such that the side portions of the working bodyextend up to the portion below the fixed portion of the substrate, it ispossible to make a design so that the volume of the working body isenlarged as a whole. As a result, the weight of the working body isincreased, thus making it possible to easily improve the sensitivity.Further, since there is employed an arrangement to utilize the lowersurface of the fixed portion of the substrate as the control member,thus to limit a displacement in an upper direction of the working body,a sensor suitable for high sensitivity physical quantity measurement canbe realized with a simple structure.

(2) If there is employed in the above described sensor an arrangement toutilize the inside surface of the pedestal as the control member, thusto limit a displacement in a lateral direction of the working body, asensor suitable for high sensitivity physical quantity measurement canbe realized with a simple structure.

(3) If there is employed in the above described sensor an arrangement tofix the pedestal so that the lower surface of the working body and apredetermined control surface are opposite with a predetermined spacingtherebetween, thus permitting a displacement in a lower direction of theworking body to limitatively fall within a predetermined range by thiscontrol surface, a sensor suitable for high sensitivity physicalquantity measurement can be realized with a simple structure.

(4) If there is employed in the above described sensor an arrangement tomake a design so that the distance between the working point defined atthe central portion of the upper surface of the substrate falls withinan optimum range, detection sensitivities in respective axial directionsof three dimensions can be uniform.

INDUSTRIAL APPLICABILITY

A force sensor, an acceleration sensor, and a magnetic sensor accordingto this invention can be mounted and utilized in all industrialmachines. Since high precision measurement can be conducted with a smalland low cost sensor, application of an automotive vehicle or anindustrial robot is expected. Particularly, the acceleration sensorserves, as described as the embodiment, as an ideal device for use inwhich this sensor is mounted in an automotive vehicle to produce anoperating signal to an air bag.

What is claimed is:
 1. A method of testing a sensor, said sensorcomprising: a strain generative body including a working portion adaptedto undergo action of a force, a fixed portion fixed to a sensor body anda flexible portion having flexibility, said flexible portion surroundingsaid working portion and said fixed portion surrounding said flexibleportion, a working body fixed to said working portion on a lower surfaceof said strain generative body, said working body being suspended fromthe fixed portion with three-dimensional freedom so that a spacialdeviation of said working body is produced by exerting a force thereto,detector means for transforming said spacial deviation to an electricsignal which indicates a direction and a magnitude of the exerted force,wherein said method comprises the steps of: defining an XYZthree-dimensional coordinate system so that an XY-plane extends along anupper surface of said strain generative body and an origin locates onsaid working portion, preparing a first electrode and a second electrodeon the upper surface of said strain generative body, said firstelectrode being located on an upper surface of said flexible portion ina positive area of the X-axis and said second electrode being located onthe upper surface of said flexible portion in a negative area of theX-axis, preparing a first opposite electrode facing said first electrodewith a distance and a second opposite electrode facing said secondelectrode with a distance, said first opposite electrode and said secondopposite electrode being fixed to the sensor body, producing a spacialdeviation along the X-axis of said working body by applying a firstvoltage between said first electrode and said first opposite electrodeand applying a second voltage between said second electrode and saidsecond opposite electrode so that a repulsive force is produced betweena pair of electrodes and an attractive force is produced between anotherpair of electrodes on the basis of coulomb force, and detecting anelectric signal transformed by said detector means while said spacialdeviation is produced, thus to test a detecting function along theX-axis of said sensor based on a relationship between the detectedelectric signal and the applied voltages.
 2. A method of testing asensor as set forth in claim 1, wherein the method further comprises thesteps of: preparing a third electrode and a fourth electrode on theupper surface of the strain generative body, said third electrode beinglocated on the upper surface of the flexible portion in a positive areaof the Y-axis and said fourth electrode being located on the uppersurface of the flexible portion in a negative area of the Y-axis,preparing a third opposite electrode facing said third electrode with adistance and a fourth opposite electrode facing said fourth electrodewith a distance, said third opposite electrode and said fourth oppositeelectrode being fixed to the sensor body, producing a spacial deviationalong the Y-axis of the working body by applying a third voltage betweensaid third electrode and said third opposite electrode and applying afourth voltage between said fourth electrode and said fourth oppositeelectrode so that a repulsive force is produced between a pair ofelectrodes and an attractive force is produced between another pair ofelectrodes on the basis of coulomb force, and detecting an electricsignal transformed by said detector means while said spacial deviationis produced, thus to test a detecting function along the Y-axis of saidsensor based on a relationship between the detected electric signal andthe applied voltages.
 3. A method of testing a sensor as set forth inclaim 2, wherein the method further comprises the steps of: producing aspacial deviation along the Z-axis of said working body by applying afirst voltage between the first electrode and the first oppositeelectrode, applying a second voltage between the second electrode andthe second opposite electrode, applying a third voltage between thethird electrode and the third opposite electrode and applying a fourthvoltage between the fourth electrode and the fourth opposite electrodeso that a first coulomb force is produced between the first electrodeand the first opposite electrode, a second coulomb force is producedbetween the second electrode and the second opposite electrode, a thirdcoulomb force is produced between the third electrode and the thirdopposite electrode and a fourth coulomb force is produced between thefourth electrode and the fourth opposite electrode, said first, second,third and fourth coulomb force having a same polarity, and detecting anelectric signal transformed by said detector means while said spacialdeviation is produced, thus to test a detecting function along theZ-axis of said sensor based on a relationship between the detectedelectric signal and the applied voltages.
 4. A method of testing asensor as set forth in claim 2, wherein polarities of the first, second,third and fourth voltages are varied with time.
 5. A method of testing asensor as set forth in claim 4, wherein the method further comprises thefurther steps of: applying another voltage between said first electrodeand said first opposite electrode and applying another voltage betweensaid second electrode and said second opposite electrode so that anotherattractive-polarity coulomb force is produced between one of said firstand first opposite or second and second opposite electrodes and anotherattractive-polarity coulomb force is produced between the other thereof,said other coulomb forces constituting another said force for producinganother spacial deviation of said working body; detecting anotherelectric signal transformed by said detector means while other saidother spacial deviation is produced; and testing said detecting alongsaid Z-axis from a relationship between said other electric signal andsaid other applied voltages.
 6. A method of testing a sensor as setforth in claim 1, wherein the method further comprises the steps of:producing a spacial deviation along the Z-axis of the working body byapplying a first voltage between the first electrode and the firstopposite electrode and applying a second voltage between the secondelectrode and the second opposite electrode so that a first coulombforce is produced between the second electrode and the first oppositeelectrode and a second coulomb force is produced between the secondelectrode and the second opposite electrode, said first coulomb forceand said second coulomb force having a same polarity, and detecting anelectric signal transformed by said detector means while said spacialdeviation is produced, thus to test a detecting function along theZ-axis of said sensor based on a relationship between the detectedelectric signal and the applied voltages.
 7. A method of testing asensor as set forth in claim 1, wherein polarities of the first voltageand the second voltage are varied with time.
 8. A method of testing asensor, said sensor comprising: a sensor body; a strain generative bodyincluding a working potion for receiving a force, a flexible portionabout said working portion and having flexibility to said force, and afixed portion about said flexible portion and fixed to said sensor body;a working body fixed to said working portion on a lower surface of saidstrain generative body, whereby said working body is suspended from saidsensor body with three-dimensional freedom so that spacial deviation ofsaid working body is produced by applying said force thereto; anddetector means for transforming said spacial deviation into an electricsignal that indicates a direction and a magnitude of said force, saidmethod comprising the steps of: defining an XYZ three-dimensionalcoordinate system so that an XY-plane thereof is on an upper surface ofsaid strain generative body and an origin is located on said workingportion thereof; providing a first electrode and a second electrode onsaid upper surface of said strain generative body on said flexibleportion thereof, said first electrode being located in a positive areaof said X-axis and said second electrode being located in a negativearea of the X-axis; providing on said sensor body a first oppositeelectrode facing said first electrode from a distance and a secondopposite electrode facing said second electrode from a distance;applying a first voltage between said first electrode and said firstopposite electrode and applying a second voltage between said secondelectrode and said second opposite electrode so that a firstrepulsive-polarity coulomb force is produced between one of said firstand first opposite or second and second opposite electrodes and a secondattractive-polarity coulomb force is produced between the other thereof,said first and second coulomb forces constituting said force forproducing said spacial deviation of said working body; detecting anelectric signal transformed by said detector means while said spacialdeviation is produced; and testing said detecting along said X-axis fromrelationship between said electric signal and said first and secondapplied voltages.
 9. A method of testing a sensor as set forth in claim8, wherein the method further comprises the further steps of: providinga third electrode and a fourth electrode on said upper surface of saidstrain generative body on said flexible portion thereof, said thirdelectrode being located in a positive area of said Y-axis and saidfourth electrode being located in a negative area of the Y-axis;providing on said sensor body a third opposite electrode facing saidthird electrode from a distance and a fourth opposite electrode facingsaid fourth electrode from a distance; applying a third voltage betweensaid third electrode and said third opposite electrode and applying afourth voltage between said fourth electrode and said fourth oppositeelectrode so that a third repulsive-polarity coulomb force is producedbetween one of said third and third opposite or fourth and fourthopposite electrodes and a fourth attractive-polarity coulomb force isproduced between the other thereof, said third and fourth coulomb forcesconstituting still another said force for producing still anotherspacial deviation of said working body; detecting still another electricsignal transformed by said detector means while said still anotherspacial deviation is produced; and testing said detecting along saidY-axis from a relationship between said still another electric signaland said third and fourth applied voltages.
 10. A method of testing asensor as set forth in claim 9, wherein said polarities of all saidvoltages are varied over time.
 11. A method of testing a sensor as setforth in claim 8, wherein said polarities of all said voltages arevaried over time.
 12. A method of testing a sensor, said sensorcomprising: a sensor body; a strain generative body including a workingpotion for receiving a force, a flexible portion about said workingportion and having flexibility to said force, and a fixed portion aboutsaid flexible portion and fixed to said sensor body; a working bodyfixed to said working portion on a lower surface of said straingenerative body, whereby said working body is suspended from said sensorbody with three-dimensional freedom so that spacial deviation of saidworking body is produced by applying said force thereto; and detectormeans for transforming said spacial deviation into an electric signalthat indicates a direction and a magnitude of said force, said methodcomprising the steps of: defining an XYZ three-dimensional coordinatesystem so that an XY-plane thereof is on an upper surface of said straingenerative body and an origin is located on said working portionthereof; providing a first electrode and a second electrode on saidupper surface of said strain generative body on said flexible portionthereof, said first electrode being located in a positive area of saidX-axis and said second electrode being located in a negative area of theX-axis; providing on said sensor body a first opposite electrode facingsaid first electrode from a distance and a second opposite electrodefacing said second electrode from a distance; applying a first voltagebetween said first electrode and said first opposite electrode andapplying a second voltage between said second electrode and said secondopposite electrode so that a first attractive-polarity coulomb force isproduced between one of said first and first opposite or second andsecond opposite electrodes and a second attractive-polarity coulombforce is produced between the other thereof, said first and secondcoulomb forces constituting said force for producing said spacialdeviation of said working body; detecting an electric signal transformedby said detector means while said spacial deviation is produced; andtesting said detecting along said Z-axis from a relationship betweensaid electric signal and said first and second applied voltages.
 13. Amethod of testing a sensor as set forth in claim 12, wherein the methodfurther comprises the further steps of: providing a third electrode anda fourth electrode on said upper surface of said strain generative bodyon said flexible portion thereof, said third electrode being located ina positive area of said Y-axis and said fourth electrode being locatedin a negative area of the Y-axis; providing on said sensor body a thirdopposite electrode facing said third electrode from a distance and afourth opposite electrode facing said fourth electrode from a distance;applying a third voltage between said third electrode and said thirdopposite electrode and applying a fourth voltage between said fourthelectrode and said fourth opposite electrode so that a thirdrepulsive-polarity coulomb force is produced between one of said thirdand third opposite or fourth and fourth opposite electrodes and a fourthattractive-polarity coulomb force is produced between the other thereof,said third and fourth coulomb forces constituting still another saidforce for producing still another spacial deviation of said workingbody; detecting still another electric signal transformed by saiddetector means while said still another spacial deviation is produced;and testing said detecting along said Y-axis from a relationship betweensaid still another electric signal and said third and fourth appliedvoltages.
 14. A method of testing a sensor as set forth in claim 13,wherein said polarities of all said voltages are varied over time.
 15. Amethod of testing a sensor as set forth in claim 13, wherein the methodfurther comprises the further steps of: providing a third electrode anda fourth electrode on said upper surface of said strain generative bodyon said flexible portion thereof, said third electrode being located ina positive area of said X-axis and said fourth electrode being locatedin a negative area of the X-axis; providing on said sensor body a thirdopposite electrode facing said third electrode from a distance and afourth opposite electrode facing said fourth electrode from a distance;applying a third voltage between said third electrode and said thirdopposite electrode and applying a fourth voltage between said fourthelectrode and said fourth opposite electrode so that a thirdrepulsive-polarity coulomb force is produced between one of said thirdand third opposite or fourth and fourth opposite electrodes and a fourthattractive-polarity coulomb force is produced between the other thereof,said third and fourth coulomb forces constituting still another saidforce for producing still another spacial deviation of said workingbody; detecting still another electric signal transformed by saiddetector means while said still another spacial deviation is produced;and testing said detecting along said X-axis from a relationship betweensaid still another electric signal and said third and fourth appliedvoltages.
 16. A method of testing a sensor as set forth in claim 15,wherein said polarities of all said voltages are varied over time.
 17. Amethod of testing a sensor as set forth in claim 12, wherein saidpolarities of all said voltages are varied over time.